When using Fastbay in standard mode (with business policies support being deactivated) – payment, shipping and return methods are sent directly by the module for each product based on the configurations made in the module itself.
In this condition, if the business rules support is enabled on eBay, many new rules will be created automatically to group products, if necessary. This is not an error, however, the eBay rules will not be of any use as the module will send the data per product by bypassing them.
Furthermore, if you already have products on eBay with previously created and linked rules on eBay, these will therefore be overridden by the new rules, unless you configure the type of product update in “sync quantity or quantity/price” mode.
If you need to maintain the use of eBay business policies, the module offers the possibility to link existing eBay rules to the eBay categories mapped in the module, see the relevant section for more information.
In this case, make sure that all your module’s eBay categories are mapped with proper shipping policies.