Technology / Amazon
Amazon integration, the parts vendors gloss over
Selling on Amazon involves three channels with three different integration shapes: FBA, MCF, and FBM. Each one breaks differently. This guide is a field-grade walkthrough of the Selling Partner API surface, prep work that actually has to happen in a 3PL, and what an IPI score does to your wallet.
TL;DR
- SP-API is OAuth, REST, and report-driven. Order events stream through the Notifications API. Inventory and reporting still go through async report jobs.
- FBA is fast for Amazon orders but slow to react to your operations. Inbound, prep, FNSKU labeling, and IPI are where most 3PL hours go.
- MCF is a fulfillment back-end for non-Amazon orders. It works for Shopify and DTC, but bundling, brand-stickered packaging, and gift messages are constrained.
- FBM and Seller-Fulfilled Prime put SLA risk back on the seller and 3PL. Late shipment rate, on-time delivery, and valid tracking rate are the real KPIs.
Section 01
The Selling Partner API surface
SP-API replaced the old MWS API in 2022 and is now the only supported way to integrate with Seller Central programmatically. It is a collection of REST APIs grouped by section: Orders, Catalog, Listings, Inventory, FBA Inbound, FBA Inventory, Reports, Notifications, Feeds, and Finances.[1]
Auth and access
Calls require a Login with Amazon access token, which is exchanged for a short-lived bearer token. Tokens are scoped per region and per seller. Personally identifiable information access requires a separate Restricted Data Token, which is issued per call rather than per session. The RDT dance trips up integrations that forget the token expires within an hour.
Three event shapes
SP-API gives you three ways to learn that something happened.
The three SP-API surfaces solve different problems and have different rate limits.
| Surface | Shape | Use it for |
|---|---|---|
| Notifications API | EventBridge, SQS, or App-managed delivery | Order events, FBA inventory updates, listing change events |
| Reports API | Async job, returns a flat file | Settlement reports, FBA inventory snapshots, returns reports |
| Direct REST | Synchronous fetch | Looking up a single order, listing item, or financial event |
Section 02
FBA prep workflows
The FBA prep workflow is the unglamorous core of any seller relationship with Amazon. Get it wrong and inbound shipments are rejected, fees are charged, and listings are suppressed. Get it right and most of the day-to- day work is invisible.
What "prep" actually means
Amazon's prep requirements depend on the product category and the unit shape. Liquids must be poly-bagged with a suffocation warning. Sets must be labeled "Sold as Set, Do Not Separate". Apparel must be poly-bagged. Sharp items must be capped. The full matrix is published, but in practice every new SKU goes through a "first inbound, see what gets flagged" cycle.[4]
- Step 1FNSKU labeling
Each unit gets a barcode unique to that seller's SKU at that warehouse. Stickering can be done by the seller, the 3PL, or Amazon for a per-unit fee.
- Step 2Unit prep
Poly-bagging, bubble-wrapping, taping, or suffocation labeling per the prep requirement matrix.
- Step 3Carton building
Pack to the FBA carton size and weight rules. Master cartons must not exceed 50 lb without a team-lift sticker.
- Step 4Inbound shipment plan
Create the plan in Seller Central, get the destination FCs assigned, print the box labels. Inbound Placement Service fees apply when you do not split.
- Step 5Pickup and pod scan
Carrier picks up. The first scan at the FC opens the inbound, which is when units start counting toward IPI.
Inbound Placement Service
Since 2024, Amazon charges an Inbound Placement Service fee when sellers ship to a single FC instead of splitting across multiple destinations.[10] The fee is per-unit and depends on tier. For a 3PL building shipments, the practical effect is that the savings of consolidating inbounds into a single carrier load have to be weighed against the per-unit IPS fee. Most large brands now run a hybrid: high velocity SKUs ship multi-destination, slow movers ship single-destination and accept the fee.
Section 03
Multi-Channel Fulfillment, when it works and when it does not
MCF lets sellers fulfill non-Amazon orders out of FBA inventory. It is attractive because it reuses a network you are already paying for. It is also constrained.[2]
MCF capabilities as of 2026. Always check Seller Central for current per-program rules.
| Capability | MCF reality |
|---|---|
| Service speed | Standard, Expedited, Priority, with Standard typically two business days in metros |
| Branded packaging | Generic Amazon-branded outer carton by default; unbranded box add-on available |
| Gift messaging | Not supported |
| Bundles | Limited; multi-pack must be set up as a separate FBA SKU |
| Returns | Goes to FBA returns, gets graded, may or may not be re-listed automatically |
| Inventory pool | Shared with FBA, so a Prime spike can starve MCF and vice versa |
| Order injection | SP-API CreateFulfillmentOrder, or via Shopify, BigCommerce, and similar app integrations |
“MCF is a fulfillment lever, not a replacement for a 3PL. It works best for brands whose unit economics already support FBA and whose off-Amazon volume is bursty rather than steady.”
Cost shape
MCF fees are per-unit, scaled by service speed. They are visible per SKU in Seller Central. Compared to a 3PL, MCF tends to be cheaper for low-cube items at moderate volume and more expensive for heavy or low-margin items where the per-unit cost dominates.[9]
Section 04
FBM and Seller-Fulfilled Prime
Fulfilled by Merchant covers any Amazon order shipped from outside the FBA network. The seller, or the 3PL acting for the seller, is responsible for picking, packing, labeling, and confirming shipment within the offer's promised handling time.
The metrics that matter
Three account-health metrics decide whether an FBM seller stays on the platform: late shipment rate (under 4 percent), valid tracking rate (above 95 percent), and on-time delivery rate (above 97 percent for Prime).
Amazon Account Health thresholds tracked by Seller Central.
| Metric | Threshold | Where it breaks |
|---|---|---|
| Late shipment rate | Under 4% | Cutoff time slippage, manual ship-confirms |
| Valid tracking rate | Above 95% | Tracking number not returned by carrier in time, wrong format |
| On-time delivery (Prime) | Above 97% | Carrier service-level missed, not just label-printed |
| Cancellation rate | Under 2.5% | Inventory desync, oversold listings |
| Order defect rate | Under 1% | Damages, wrong item, A-to-Z claims |
Seller-Fulfilled Prime
SFP is the program that lets a non-FBA seller earn the Prime badge by meeting Prime-grade SLAs from their own warehouses.[6] In practice this requires same-day handoff for orders before the regional cutoff, weekend pickup coverage, and a nationwide carrier mix that includes two-day capable services. For 3PLs, SFP is operationally more demanding than FBM and is not appropriate for every brand.
Section 05
FNSKU labeling, the right way
FNSKU is Amazon's per-seller, per-SKU barcode. It is what the FC scans at receipt to attribute units to a specific Seller Central account. The alternative is "stickerless commingled" inventory, which Amazon stopped accepting for most categories years ago.[7]
Three places the labeling can happen:
- At the manufacturer. Cheapest, but irreversible. If you ever switch fulfillment models, those units are stuck.
- At the 3PL. Right answer for most brands. Lets the 3PL switch a unit between FBA, FBM, MCF, and retail without rework.
- By Amazon (FBA Label Service). Per-unit fee. Convenient, but the math rarely works at volume.[7]
Section 06
Hazmat compliance and the IPI score
Hazmat is not a checkbox
Amazon classifies dangerous goods using a combination of UN numbers, ORM-D classifications, and proprietary internal categories. Aerosols, lithium batteries, alcohol-containing personal care, magnetic items, and pressurized cartridges are the most common hazmat-flagged categories.[5] Each one needs a Safety Data Sheet, an Exemption form, and per-unit labeling. Items pending hazmat review do not sell, even if the listing is live.
IPI explained without the marketing
The Inventory Performance Index is a 0-to-1000 score Amazon computes from four inputs: excess inventory percentage, sell-through rate, stranded inventory percentage, and in-stock rate.[3] If the score drops below the seasonal threshold (Amazon has used 400 in recent years), storage limits tighten and storage fees increase.
IPI components and how fast each one actually responds.
| Lever | What it does | Realistic time to move |
|---|---|---|
| Excess inventory | Reduce units over 90 days of cover | 30 to 90 days, via removal orders or MCF |
| Sell-through | Increase the ratio of shipped units to average on-hand | Slow, driven by demand |
| Stranded inventory | Resolve listings with inventory but no buy box | Days, fix the listing health flag |
| In-stock rate | Avoid going OOS on top SKUs | Days, replenishment cadence |
For 3PLs, the IPI lever you control most directly is stranded inventory and sell-through. Pulling stranded units back to a 3PL warehouse, repackaging, and re-listing is faster than waiting for sell-through to recover. Repeated IPI breaches are also a leading indicator that a brand is over-indexed on FBA and should split inventory.
Section 07
Capacity manager, restock limits, and the storage math
Restock limits are the harder version of IPI. The Capacity Manager governs how many cubic feet of FBA inventory a seller can hold across all warehouses, computed from sell-through, IPI, and historical compliance.[13] A brand can be in good IPI shape and still hit a storage cap, especially during Q4 when Amazon tightens limits across the network.
How limits actually move
Storage volume is measured per category (standard, oversize, apparel, footwear, dangerous goods) and limits are set monthly. Capacity Manager also exposes a reservation system: sellers can pay to reserve additional capacity ahead of a forecasted spike.[14] The brands that handle this well share three habits. They forecast cube, not just units. They review the Capacity Monitor weekly, not when the warning email arrives. They keep a percentage of inventory at the 3PL warehouse as a buffer against a sudden FBA cap reduction.
Capacity events that affect FBA throughput in 2026.
| Trigger | Effect | Recovery path |
|---|---|---|
| IPI drops below threshold | Storage limits cut, fees rise | 30 to 90 day improvement window |
| Restock limit reached | Inbound shipments rejected at the dock | Sell down or remove inventory, no shortcut |
| Q4 capacity tightening | All sellers see roughly 20 to 40 percent cut on holiday categories | Plan around it, do not fight it |
| Aged inventory surcharge | Per-cube monthly fee on units stored 365 days plus | Removal order or MCF outbound |
| Listing variation suppression | Items pulled from search until catalog issue fixed | Fix flat-file or product detail page |
The 3PL hedge
A 3PL operating alongside FBA is a hedge against capacity events that have nothing to do with the brand's own performance. When Amazon cuts holiday capacity by a third across all sellers, brands without an off-FBA pool are forced to either sell down faster than demand allows or watch their listings go stranded. Brands with a 3PL pool reroute MCF and DTC orders to the 3PL warehouse and continue advertising while FBA inventory sells down.
Section 08
Listings, the Buy Box, and Brand Registry interactions
The fulfillment integration sits next to a separate piece of work: listing and catalog hygiene. The 3PL does not own listing copy, but its operations touch the listing in ways that decide whether the SKU keeps the Buy Box.[12]
Buy Box mechanics that touch the warehouse
The Buy Box (now called the Featured Offer) goes to the seller Amazon trusts most for that ASIN at that moment. The signals Amazon weights include fulfillment method (FBA wins by default), price, in-stock rate, defect rate, and seller performance. A clean fulfillment record is a Buy Box input, which means a 3PL that lets late shipments pile up indirectly costs the brand the Buy Box and the revenue that flows from it.
For FBM and SFP listings, the warehouse signal is direct. Late ship-confirm, cancellations, and return rate all feed the seller-performance score. We treat each metric as a hard contract per SKU and route exceptions to a human before the metric trips.
Brand Registry and the integrity layer
Brand Registry is Amazon's system for verified brand owners.[11] It enables A+ Content, Sponsored Brands ads, Project Zero takedowns, and Transparency, the per-unit serial-number anti-counterfeit program. Transparency is the program with the deepest 3PL impact. It requires a unique Transparency code on every unit, in addition to the FNSKU. The 3PL applies the code at receive (or at prep), and Amazon scans both barcodes at the FC. A unit without a valid Transparency code is rejected.
Brand Registry programs and their fulfillment touch points.
| Brand Registry program | Operational impact for the 3PL | Cost shape |
|---|---|---|
| Brand Registry baseline | Access to ASIN locking and counterfeit reports | Free, requires registered trademark |
| Transparency | Per-unit code application at prep, dual barcode scan at FC | Per-unit code fee |
| Project Zero | Takedown authority, no operational change | Free for invited sellers |
| Brand Gating | Invitation-only resellers, no operational change | Per-application fee |
| A+ Content | No operational change, listing only | Free |
| Vine reviews | Unit reservation for Vine reviewers, ships out as MCF or FBM | Per-enrollment fee |
“The 3PL does not write the listing. It does, however, decide whether the listing keeps the Buy Box. Late ship and high defect rate kill the Buy Box faster than any pricing competitor.”
Listing variations and the SKU map
Amazon parent-child relationships (variations) live above the SKU. A single parent ASIN can have dozens of size and color child ASINs, each with its own FNSKU. The 3PL maps each child FNSKU to the WMS SKU. A common mistake is a 1:N mapping (one Amazon child ASIN to multiple WMS SKUs) which loses audit trail for inventory disputes. We enforce 1:1 from FNSKU to WMS SKU and surface any ambiguity at onboarding rather than during a dispute.
Section 09
The operating model across FBA, MCF, FBM, and DTC
Most brands above $5M in revenue run a mix. The interesting question is how you split inventory and which channel gets the next unit when they compete. The wrong answer is to assign units to channels at receive time. The right answer is to keep units pooled and decide allocation on demand.
A hybrid pool, not silos
We hold inventory at the 3PL warehouse as a pooled bucket and push to FBA on a forecast-driven cadence. The forecast considers the FBA velocity (units sold per day on Amazon), the MCF velocity (Amazon's MCF-fulfilled orders for non-Amazon channels), the DTC velocity, and the Capacity Manager headroom. A scheduled job computes how many units of each SKU should be at FBA next week, and the warehouse builds and ships an inbound that hits exactly that target. Anything above the target stays at the 3PL warehouse and serves DTC and FBM.
Channel switching at the unit level
Because we apply FNSKU at the 3PL, we can flip a unit between FBA, FBM, MCF, and DTC by re-routing rather than re-prepping. A unit destined for FBA that gets caught by a Capacity Manager cap can be redirected to FBM in the same shift. A unit pulled back from FBA in a removal order can be relisted as FBM the same day. This flexibility is the single biggest reason brands keep a 3PL warehouse alongside FBA.
Reporting and reconciliation
Reconciliation runs daily for FBA inventory and weekly for the settlement report. The FBA inventory report often disagrees with the 3PL outbound record by a few units across a week (in transit, at the FC dock, or recently received). Both numbers need to be tracked separately so an accidental double-count does not show up as a mystery shrink event. The settlement report drives the brand's revenue and our chargeback flow, so we keep an immutable copy of every weekly settlement file.
The settlement reconciliation also catches Amazon-side fee changes that happen quietly. Storage fees, removal fees, return processing fees, and long-term storage fees move multiple times a year. Without a per-unit audit, the brand only sees the total monthly bill move and assumes it is volume. With the audit, we attribute each fee delta to a specific program change, which is the difference between accepting a price increase and negotiating around it.
Section 10
Cross-border, taxes, and the marketplace facilitator role
For brands selling outside the US, two operational facts are worth knowing early. Amazon collects sales tax for sellers in every US state where it is legally required, in its role as a marketplace facilitator. The seller still needs to maintain nexus filings, but the per-order collection is Amazon's responsibility, not the seller's. For a 3PL, the practical effect is that the order total includes Amazon-collected tax, and the settlement report is where the brand sees the gross receipt versus the post-tax-remittance net.
Cross-border FBA
Selling internationally on Amazon involves a separate seller account per region (NA, EU, UK, JP, AU). Inventory does not flow between regions automatically. A US brand selling into the EU has to either import inventory into an EU FBA warehouse, use the European Fulfillment Network for cross-border orders within Europe, or run FBM out of an EU 3PL. The 3PL integration shape is the same per region; only the SP-API endpoint, marketplace IDs, and tax registration change.
VAT and IOSS for EU
For EU sales below 150 euros, Amazon participates in the Import One-Stop Shop (IOSS), collecting VAT at the order and remitting on the seller's behalf. Above 150 euros, the seller is responsible for VAT registration in each country of sale or for using the One-Stop Shop scheme. The 3PL handling cross-border outbound has to mark IOSS-eligible shipments correctly on the customs paperwork; getting this wrong leads to either the buyer being double-billed or the parcel being returned at the destination border.
Section 321 and de minimis
For US-bound shipments from non-US warehouses, Section 321 used to allow duty-free entry below $800 per shipment per day per consignee. The 2025 policy changes have narrowed this, with country-specific carve-outs and additional documentation requirements. Brands fulfilling Amazon US orders from China-located inventory need to either move inventory to a US warehouse before listing, or accept formal entry duties on every shipment. The 3PL operating the inbound has to track these on a per-SKU basis because the rule changes more than once a year.
Section 11
The annual operating rhythm
Amazon as a channel has its own calendar. Q4 is the peak; Q1 is when storage fees and Long-Term Storage assessments hit; spring and summer are when sellers can replenish without capacity pressure. A 3PL that runs the Amazon channel well plans its operations against this calendar rather than against the brand's marketing calendar.
Q4 readiness
The capacity squeeze in October and November rewards preparation done in August. By August, every SKU that will be in the holiday push needs to have its prep matrix nailed down, its FNSKU labels in stock, and its inbound placement strategy decided. Brands that wait until October to lock these decisions get caught between rejected inbounds and a tight on-shelf date. We start Q4 reviews in July with the brand operator and the demand planner.
January and the long-term storage assessment
On the 15th of every month, Amazon assesses Long-Term Storage Fees on units that have been in FBA for more than 365 days. Q1 is the most painful month because the assessment hits right after Q4, when slow-moving holiday inventory has not sold through. A removal order placed in November lands in time to avoid the January assessment; a removal placed in late December does not. We schedule the November removal review as a fixed annual ritual.
The summer optimization window
Summer is when storage limits are most generous, capacity is available, and Amazon-side fee changes have not yet rolled into the year. It is the right time to relabel SKUs, consolidate listings, audit variation parents, and clean up stranded inventory. Brands that do this work in summer go into Q4 with a tighter listing surface and a more responsive inbound flow. Brands that skip it spend Q4 fighting catalog problems instead of selling.
Talk to us
Run FBA, MCF, and FBM out of one operation
Warpspeed handles SP-API integration, FBA inbound prep, FNSKU labeling, and FBM SLAs from the same warehouse. We can route SKU-level inventory between FBA and your DTC channel based on velocity and IPI signals.
Sources
- [src-1]Selling Partner API overview— Amazon
- [src-2]Multi-Channel Fulfillment overview— Amazon Seller Central
- [src-3]FBA Inventory Performance Index— Amazon Seller Central
- [src-4]FBA prep service requirements— Amazon Seller Central
- [src-5]FBA dangerous goods program— Amazon
- [src-6]Seller-Fulfilled Prime— Amazon
- [src-7]FNSKU labeling requirements— Amazon Seller Central
- [src-8]SP-API rate limits— Amazon
- [src-9]MCF fee changes for 2024— Amazon Seller Central
- [src-10]FBA inbound placement service— Amazon
- [src-11]Amazon Brand Registry— Amazon
- [src-12]Buy Box eligibility and Featured Offer— Amazon Seller Central
- [src-13]FBA storage limits and capacity manager— Amazon Seller Central
- [src-14]Restock Limits and capacity tiers— Amazon Seller Central