To set your eBay store category for a listing: 

1. Navigate to Inventory and choose inventory management.

2. Click into a product using the binoculars icon.

3. Choose the 'listing attributes tab' and choose 'eBay' 

4. Scroll down to the optional attributes section. 

5. You will see a attribute 'eBay Store Category Id'. If you do not see this attribute, choose the green 'Add attribute' button. 

6. Enter your store category ID or choose 'Find Store Category'.