The externalAppData field is an object designed to hold additional data related to external integrations.
This object can contain the following keys, which are currently supported:
externalCustomerId: A string representing the customer ID of the user in an external payment provider integration. This ID is used to link the user's account within the system to their corresponding account in the external payment provider.
If no information is available, the externalAppData object will be null. It's a part of the response only if request is called with include.externalAppData query parameter.