A Fully Qualified Domain Name (FQDN) is a unique identifier assigned to each Wix service entity.
The standard FQDN naming structure looks like: wix.<domain?>.<product>.<version>.<entity>.
For example:
wix.ecom.v1.cart.wix.multilingual.machine.v3.translatable_content.An entity's FQDN is returned in every webhook (except for legacy webhooks) and may be required in endpoints that work with entities from other Wix services.