Sometimes the lister wouldn't recognize category number and you would get the following error in the lister:
 

LISTING FAILED
{"category_id":["Not a valid integer."]}

OR

Please fix the following. Category_id - Missing data for required field.

Your Yaballe user is not connected to eBay (token disconnected). To connect go to Yaballe SETTINGS > ADVANCED > ADVANCED ACCOUNTS SETTINGS > RECONNECT TO EBAY (red button).

There are no recognizable existing similar listings in eBay for us to refer to.

In such case you have to do the following:

Copy the title from one of the items the lister suggests under "Other Sellers" and copy the category number from that item manually like this: