The 3PL onboarding process explained: a step-by-step implementation checklist

July 2026 · 8 min read · Angler Fulfilment

Share on X LinkedIn Facebook WhatsApp

How long a move to a 3PL takes depends far more on your preparation than on the warehouse. A seller with a few hundred SKUs can be taking orders within days of their stock arriving, if the preparation happens in parallel with the physical move rather than after it. When onboarding slips, it is almost never the warehouse that caused it. It is a product catalogue that has never had dimensions in it, stock that arrives without a delivery note, or a channel integration nobody had the admin password for.

Step 1: the catalogue

This is where the whole project is won or lost. Export your product list and add, for every single SKU:

• A unique SKU code that matches across every sales channel you sell on. If Shopify calls it BLU-TS-M and eBay calls it tshirt-blue-medium, fix that before you move, not after
• A scannable barcode: EAN, UPC or GTIN. If a product has none, decide now whether you are buying barcodes or having the 3PL label them, because the second option is a per-unit charge
• Dimensions and weight of the packed unit, measured, not estimated. These drive box selection and postage, and a wrong weight becomes a carrier surcharge on every order of that SKU
• Whether it is fragile, hazardous, temperature-sensitive, battery-containing or restricted. Say so now. Lithium batteries and aerosols have shipping rules that will surface eventually, better on day two than on the first customer order
• Its bundle or kit composition, if it is a multipack, and whether it is stored assembled or built to order

Send this file to your 3PL before your stock moves. A good one will come back with questions. Questions at this stage are a good sign.

Step 2: channels and integrations

Every channel you sell on needs to push orders to the warehouse and receive stock levels back. Practically, that means:

• Admin-level access to each store. Not a staff account, but a genuine admin login, or the ability to install an app
• Deciding where stock truth lives. It has to be one system. Two systems both believing they are authoritative is how you oversell
• Confirming which order statuses trigger fulfilment, and what happens to orders that are flagged for fraud review, on hold, or awaiting payment
• Deciding how tracking numbers get back to the customer: through the channel, through your own email, or both
• Agreeing what happens to pre-orders and backorders, which almost always break first because the rules differ per channel

We charge a published £150 to set your integrations up, once, however many channels you connect. A setup charge you can see before you sign is not the problem. What to watch for is the fee that only appears at contract stage, and the one that looks like setup but recurs every month as a platform or account management charge. Ask which of the two you are being quoted. See the platforms we connect to.

Step 3: packaging and the unboxing decision

Decide before the stock arrives, because changing it afterwards means repacking.

• Plain or branded outer packaging, and if branded, is it already printed and where is it
• Which box and bag sizes cover which products, and who chooses when an order is borderline
• Inserts, thank-you cards, samples, returns labels: what goes in every parcel, what goes in some, and what the rule is
• Whether you need packaging-material storage in your quote. Branded boxes take space and space is billed
• Your fragile-item standard, in writing. “Wrap it well” is not a standard. “Two layers of bubble wrap, void fill to the top, fragile tape” is

Step 4: moving the stock

Do not send everything at once. Send your top 20 SKUs by order volume first. They are the ones that need to be live on day one, they prove the process end to end, and if something is wrong with the receiving flow you find out on twenty SKUs rather than four hundred.

For each delivery, agree an advance shipping notice: what is coming, how many units of each SKU, how many cartons, when it will arrive, and who the carrier is. Book the delivery slot. Label the outside of each carton with SKU and quantity. Single-SKU cartons wherever you can: mixed cartons cost more to receive and take longer to check.

Expect a discrepancy report. Almost every first delivery has one, because almost every seller's stock figures are slightly wrong. That is what the process is for. Our own commitment is stock booked in within 48 hours of arrival, and we send the discrepancy report whether or not it is flattering to either side.

Step 5: test orders

Do not skip this and do not let anyone talk you into skipping it. Place real orders through every channel, and check each one all the way through:

• Did the order reach the warehouse, with the right SKU and quantity?
• Was the right item picked, and packed to your standard?
• Did the tracking number reach the channel and the customer?
• Did the stock level decrement correctly, on every channel, not just the one you ordered from?
• Now process a return on one of them, end to end. Returns are where integrations break most often and where nobody ever tests

Test at least one multi-item order and one order containing a bundle. Single-item test orders pass on systems that will fail in production.

Step 6: cutover

• Pick a cutover moment and write down which orders belong to the old process and which to the new. Order number is usually the cleanest boundary
• Update your returns address everywhere: website, channel settings, packing inserts, auto-reply emails, marketplace policies. This is the single most commonly missed item on this list
• Update delivery estimates on your storefront if the cut-off time has changed
• Agree who your named contact is and how you reach them when something is wrong at 4pm on a Friday
• Keep a small buffer of your bestsellers accessible for the first fortnight. You almost certainly will not need it. It costs very little to have it

What good looks like in the weeks after go-live

Stock accuracy above 99%, dispatch confirmations arriving when they should, and no customer emails asking where their order is. If you are getting those three, the move worked. If stock accuracy is drifting, stop and find the cause immediately. Drift compounds, and by month three it becomes a full recount.

3PL onboarding, answered straight

How long does 3PL onboarding take?

It depends mostly on your product data and how quickly your stock moves. This checklist works in six steps: catalogue, channels and integrations, packaging, moving the stock, test orders and cutover, and the first three can run while your stock is still with you. With us, onboarding starts the day you say yes and you can take orders within 3 days of your stock arriving. What stretches a move is almost never the warehouse. It is product data that has to be cleaned first.

What does the 3PL onboarding process involve?

Six stages: getting the catalogue accurate, connecting the sales channels, deciding the packaging, moving the stock, running test orders end to end, and the cutover itself. Each one has an owner and a date, and the ones people skip are the test orders and the packaging decision.

Can I switch fulfilment provider without pausing sales?

Yes, and you should not have to pause. Stock moves in a planned sequence rather than all at once, test orders prove the route before any real order uses it, and the cutover happens when both sides are already working. A provider who asks you to stop trading for a week is telling you something about how they run a move.

What do I need to prepare before onboarding starts?

A clean product list with barcodes, dimensions and weights; the logins or permissions for each sales channel; your packaging decision or the packaging itself; and a stock count you actually believe. The first and the last are where most delays live.

What does onboarding cost?

Onboarding itself is free with us, and there is no minimum spend. Connecting your sales channels is a single 150 pound charge that covers every channel and never recurs.