The WholeCell-Ecommerce integrations work mostly the same way where the following are synced:
Inventory quantities (WholeCell → E-commerce)
Listings (E-commerce → WholeCell)
Orders (E-commerce → WholeCell)
Shipments (WholeCell → E-commerce)
There are some differences in how the integration works for these channels which you will find just by looking at the respective E-commerce settings pages and reading the Help articles, but the ones above are common to the integrations.
Enable the Integration and Import Listings to WholeCell
If you have the same SKUs for your product listings in Swappa (as an Enterprise Seller), eBay, and Back Market, those SKUs just need to be uploaded in WholeCell (your inventory too, of course). Then, enable the integration for Swappa, eBay, and Back Market, import your listings from the three channels to their respective settings pages in WholeCell.
Set Up Product Variation and SKUs in WholeCell
It's necessary that your E-commerce SKUs are also uploaded onto your WholeCell product catalog so that it will know which SKU you have an order for when one comes in and what listing to send quantity updates on.
Operation: Order Import and Listing Quantity Updates
Because you have the SKUs from the E-commerce channels in WholeCell and have now connected these systems, WholeCell can import the order from the channel and update the listing quantity, for example, the listing for iPhone X Silver 64GB Unlocked. If you had ten of these before, and now you have an open order for one piece (outstanding quantity) from Swappa showing in your WholeCell sales orders page, it will reduce the stock level/calculated quantity* to nine, which will also update eBay and Back Market. As soon as an order comes in, your calculated quantities get updated even without you getting to the order to fulfill it (scanning the stock to the order).
*Here's how the calculated quantity/stock level is computed.
Generally, the best way to start getting the integration working for you is by:
1) Uploading your inventory in WholeCell
2) Uploading your E-commerce SKUs in WholeCell
3) Enabling the E-commerce integrations and importing your listings to WholeCell.
Since the E-commerce SKUs are already uploaded in WholeCell (assuming you did step 2 before this step), as soon as the listings are imported to WholeCell, they will be automatically connected to your WholeCell product variation SKUs.
See the following articles:
Back Market - Syncing with Back Market
eBay - Syncing with eBay
Swappa Enterprise - Syncing with Swappa for Enterprise Sellers
4) Enabling the ShipStation integration if you are using it to ship orders so that your shipment tracking number can be imported to WholeCell, then WholeCell will send that to the E-commerce channel.
See: ShipStation - Syncing with ShipStation
Here's an illustration of how the order creation and fulfillment flows for an E-commerce integration with WholeCell, in this example, Swappa (the same thing happens for Back Market and eBay).
5) Fulfill the orders as they come by committing the inventory on that order.
When an order comes in and it shows "Unknown SKU" instead of the product's name from the listing, that means that SKU is not in WholeCell when the order came in. So you need to make sure all your SKUs are in WholeCell so that listing quantities can get updated. To correct this, upload your SKU and then hit 'Refresh' under "Unknown SKU" or you can edit it by connecting that unknown SKU to a product variation in WholeCell. If you commit an inventory to this order without uploading the SKU, WholeCell will not connect that committed inventory to this order item and it will create another line below the original order item. Because the inventory that you committed to the order is not associated with the listing's SKU, the updated quantity for that inventory will not be synced to the channel.
Best to have the same SKUs across all E-commerce channels
When a new listing is created in the channel, make sure to upload the new SKU in WholeCell and then import that listing in WholeCell (click the 'Sync Listings' button on the Listings tab of the channel's settings page in WholeCell)
If you have variation listings, upload all the SKUs connected to that listing in WholeCell and add them up on the channel's listing settings (see example below)