Please note this is a channel-specific article only applicable to Magento 1 and Magento 2. Make sure to also check the general troubleshooting steps for missing SKUs here.

1. Is the SKU a virtual/digital item? 

Virtual/digital items do not appear on the Channel Mapping screen.

2. Is the SKU a Variation Parent SKU?

Only child SKUs are displayed on the screen.

3. Does the SKU or Reference ID (Product ID) of the missing SKU number match with another SKU or Product ID on your channel?

As an example, if you have e.g. SKU 123 with the Reference ID 456, but your inventory also includes SKU 456 or some other SKU has the Reference ID 123, then there would be a discrepancy and the SKU would not display on the screen.

When clicking Download Listings for Magento, Linnworks would check both - SKU and Reference ID, then compare them to those that are already downloaded in the Inventory Mapping screen. To avoid duplicates, those Reference IDs and SKUs that are already in the system will not be downloaded again. 

It is important to organize your SKU and Reference ID indexing so that the scenario where Product SKU of the item will match other items Reference ID is not possible, otherwise, you will have missing SKUs in the Inventory Mapping screen. 

4. Does the item have a quantity value assigned on the channel backend?

For Magento, the API call used to update Channel Mapping will not tell Linnworks about items that do not have a stock level assigned on the channel backend. Even when the value displayed to you shows 0, it may mean that the actual stored value is NULL. Magento API will not communicate items like this over to the Linnworks mapping screen. The only way to correct this is to add a stock level to the item on the channel directly and click Download Listings (Settings > Channel Integration > Edit channel details > Listings > Download Listings) to refresh the channel mapping screen. After the item is linked to a Linnworks SKU, the Linnworks stock levels will be sent to the SKU to update and overwrite it whether needed.