How do I keep stock in sync across all channels?

Overselling happens in the gap between two events: an item is sold in one channel, and the other channels still show the old stock. The solution is a leading system for the one warehouse. More in ERP for online merchants.

According to the weclapp documentation, stock only goes from weclapp to the shop; weclapp is therefore the leading system for stock. After you activate the box “Automatic stock transfer to the shop”, weclapp transfers it every 5 minutes. Orders flow from the shop to weclapp when you switch on the automatic order transfer; status and tracking ID go back to the shop. Customer data flows only from the shop to weclapp, items in both directions. Prerequisite: product ID, variant ID and item number match in both systems, and the weclapp warehouses are assigned to the Shopify locations.

According to the feature table on the price page, the shop integration is included from ERP Services, the marketplace integration only in ERP Trade; the package card lists both integrations and warehouse management under ERP Trade.

Other weclapp pages describe the interval and direction differently: the integrations page speaks of real time for stock and of two-way customer synchronization, while the documentation states 5 minutes and customer data only from the shop. We follow the documentation; confirm the current state for your tenant.

According to the listing, the weclapp app in the Shopify App Store is “Free to install”. The listing itself explains the note “Additional charges may apply”: weclapp can charge external costs separately from your Shopify bill. The listing does not say which costs these are. According to the listing, to use Shopify with weclapp for free you need an ERP Trade license.

On its industry page, weclapp also writes: “No costs for interfaces and their support”. What that means for your setup is not a commitment from us; have weclapp confirm the scope in writing before signing the contract.

The weclapp list price for ERP Trade is €163 net per user per month with annual payment (weclapp list price, as of October 2026).

The price card lists “Marketplace integration (Amazon, eBay & kaufland.de etc.)” in the Trade package. The weclapp documentation describes the scope per marketplace, each with the date of the doc page. Here are the notes that the table doesn't carry.

Amazon (as of 14.11.2024): FBA and merchant-fulfilled shipping via Seller Central are supported, not Vendor Central. weclapp advises not to activate the automations at first and to test manually first.

Kaufland.de (as of 19.02.2025): Only the German storefront is supported.

eBay (as of 04.08.2021): The documentation describes order import, status feedback and listings. It does not describe a stock reconciliation there; whether your needs are covered, you clarify in advance.

Channel overview according to the weclapp documentation. According to the feature table, the shop integration is included from ERP Services, the marketplace integration only in ERP Trade.

1. An order comes in through a channel.
2. The sales order lands in weclapp, for Shopify after you switch on the automatic transfer. There you process it: pick list and shipping.
3. The stock in weclapp changes.
4. weclapp transfers the new stock to the channels: for Shopify every 5 minutes, for Amazon via reports. For Kaufland.de, the checked doc page states no interval (as of 11.10.2026).
5. For Shopify and Amazon, shipping status and tracking go back to the channel.

On invoicing, the weclapp documentation states for Kaufland.de that weclapp transfers invoices to the marketplace. For Shopify and Amazon, this page evaluates no invoicing route; clarify it before the start. This is not a substitute for tax advice. How you book channel invoices and cancellations, you clarify with your tax advisor.

A fictional example with assumed numbers: a shop sells a water bottle through three channels, Shopify, Amazon and Kaufland.de. All three ship from one warehouse with 12 units.

Assume the buffer for this item is 3 units (example assumption, not a recommendation). In the example, the channels are told only the stock minus these 3, so with 12 in the warehouse, 9 sellable units.

When warehouse stock drops to 4, the channels still show 1. If one order each now arrives on Amazon and Kaufland.de almost simultaneously, before the next stock transfer has arrived, 2 units are left in the warehouse afterwards. Both orders can be fulfilled; the buffer absorbed the time lag. It limits the risk but doesn't solve every case.

The buffer is a decision in the process, not a number or a feature from the weclapp documentation. Whether and how weclapp transfers a buffer to the channels is not documented; check it in a test. How you map it in your setup, we'll clarify in the call.

The weclapp documentation and our assessment give these limits:

• For Shopify, stock only goes from weclapp to the shop. So maintain stock only in weclapp.
• According to the documentation, stock goes to the channels at an interval (for Shopify every 5 minutes, for Amazon via reports). A gap remains between two transfers; a buffer can cushion it. We make no commitment to real time.
• We have no verified information on how the built-in integrations behave with many simultaneous orders. Plan a peak-load test.

For your own workflows running through the weclapp API, the documentation describes a queue and an upper limit for concurrent requests; details in the weclapp API documentation. For peak days, Can my ERP handle 5,000 orders in one day? provides the framework. On payouts, see How do I reconcile payouts from PayPal and others?