When you connect your online store to a 3PL's system, four things sync: incoming orders, available inventory, tracking numbers and shipment status. Everything else — your catalog, your prices, your shipping rules, your delivery promises — still lives in your store and is still your call. Understanding exactly where that line sits prevents most first-month surprises.
The four flows that do move on their own
1. Orders: from your store to the warehouse. A customer buys. The order reaches the warehouse system within seconds, with nobody downloading or uploading anything. There it becomes a pick order with its address, its items and its quantities.
2. Inventory: from the warehouse to your store. Every time something enters or leaves the warehouse, available stock updates in your store. This is the flow that prevents overselling — selling something you no longer have — and it's the most important of the four if you sell on more than one channel.
3. Tracking numbers: from the warehouse to your store. When the order is packed and the carrier label is generated, the tracking number flows back to your store and attaches to the customer's order.
4. Status: from the carrier to your store, via the warehouse. The order flips to "shipped," and from there the carrier feeds the tracking. Your customer gets their "it's on the way" email without anyone typing it.
That's the full cycle, and in a healthy integration it happens without human intervention. If you sell on a marketplace, the flow is the same: here's how the Mercado Libre connection works, for instance, and the pattern repeats on Amazon and on your own storefront.
What does NOT sync (and people assume it does)
This is the source of nearly every misunderstanding at launch:
- Your catalog. Products don't create themselves in the warehouse. Someone has to register every SKU with its description, barcode and dimensions. If your catalog has duplicate or badly named SKUs, the integration will copy them exactly as they are. Garbage in, garbage out.
- Your prices. The warehouse doesn't care and doesn't receive them. Picking a $200 order and a $20,000 order is the same operation.
- Your shipping rules. Which carrier to use, when you offer free shipping, which zones you cover and with what day promise: you configure that, and it's decided in your store, not in the warehouse.
- Your promotions and bundles. If you sell a BOGO or a pre-assembled kit, the warehouse needs to know that kit is a SKU with its own recipe. It doesn't infer it from the cart. We explain this in kitting and package pre-assembly.
- Your returns. Most integrations don't handle the trip back automatically. Reverse logistics is agreed separately, almost always with its own process.
- Your customer service. Nobody answers your customer for you.
The three places it breaks
The SKU doesn't match. This is failure number one by a wide margin. Your store calls it BLUE-M, your marketplace calls it blue_medium, and the warehouse registered it as SKU-00412. To the system those are three different products, and the order can't find its merchandise. You fix this before connecting, not after: one SKU, one code, across every channel. If you're shaky there, start with barcodes, SKUs and GTINs.
Inventory updates late. No sync is 100% instantaneous; there's a window, usually of minutes. In normal operation you won't notice. During a sales spike — a campaign, free shipping, a product going viral — that window is exactly where overselling is born. Ask how often inventory syncs before you sign, not after your first big sales day.
Nobody defined the source of truth. If your store says 40 units and the warehouse says 37, which one do you correct? The right answer is almost always the warehouse, because that's where the physical goods are. But it has to be agreed from the start, or every discrepancy becomes an argument.
What a good launch looks like
- Clean the catalog first. One SKU per product, no duplicates, real barcodes. This step is boring and it determines whether everything else works.
- Connect in read-only mode. Let the system see orders and inventory without acting yet, so you can compare against what you see.
- Reconcile opening inventory. Physical count against system before going live. Start with discrepancies and you'll carry them for months.
- Run a few test orders. Real ones, end to end, including one cancellation and one with two different items.
- Turn on one channel at a time. Your store first, then one marketplace, then the next. If something breaks, you know exactly where.
If you're coming from running it yourself, the full moving order is in how to migrate your fulfillment to a 3PL.
Frequently asked questions
How long does it take to connect my store to a 3PL? The technical connection is usually a matter of hours when the platform is one of the common ones. What takes time is the work before it: cleaning the catalog, registering SKUs and reconciling opening inventory. That work weighs more than the integration itself.
Do I need a developer? For common platforms — Shopify, WooCommerce, Mercado Libre, Amazon — no: it's configuration. If you have a custom-built store or your own ERP, then yes, someone technical gets involved, usually through an API.
What if I sell on several channels at once? That's exactly the case where the integration is worth the most. Every channel reads the same physical stock, so when a unit sells on one, it drops on all of them. It's the only practical way to avoid overselling when you have three storefronts and one inventory.
Can I keep shipping some orders myself? Yes, and it's common during the transition. What you have to watch is keeping that inventory separate from what's in the warehouse, or the two numbers will fight each other.
A good integration becomes invisible: orders come in, inventory reconciles, and you stop touching the process. A bad one gives you a new job you didn't have before. Take a look at the integrations we already have ready and, if your platform is there, the connection is the short part — we'll work through the rest with you.