This error occurs when the eBay category into which the product was mapped
requires a mandatory specific (in this case “Brand”) which is not sent by the module, because there is no mapped value in Prestashop.

Once installed, Fastbay is already pre-configured to always send the brand of the product Prestashop as the eBay “Brand”:

This works in most cases, provided that your product has a correct manufacturer.

Fastbay also allows you to “overwrite” this mapping via the tab “Specifications / conditions”,  in which the mandatory and optional values required by eBay are shown for each mapped category.

If you have overwritten the “Brand” mapping with a different Prestashop value from the manufacturer, e.g. a feature, please make sure that
that the products you are synchronising have this value, otherwise eBay will not receive any “Brand” value and will return an error.

For more information on the configuration of specifications and conditions, please refer to the help section.