This error occurs when eBay does not receive a value for the item’s dispatch time.

If the configuration you made in the module provides shipping time management by category, manufacturer or supplier :

In case of category, make sure you have assigned a valid value to the delivery time in the category mapping panel
for the category of the article you are synchronizing.

In the case of manufacturer or supplier, make sure that the product you are sending to eBay has a valid manufacturer / supplier in Prestashop and that it has a “shipping time” value properly configured in the configuration table
manufacturers / suppliers of the module.
Remember that if you add manufacturers and suppliers to the site after an initial configuration of the module,
it will always be necessary to map and configure / save the dispatch times in Fastbay.