This question has been answered on support case: 35513
Resolution:
There are two IDs needed to acquire/manage the FND endpoint:
Database User - account used when connecting to the database and must have the appropriate privileges to manage the Oracle Applications tables.
Application User - account used when managing Oracle applications. You can use any user that has already been created in Oracle Applications and that has the System Administrator standard responsibility.
The DB User must be the APPS account based on a requirement from Oracle and the Application User is hardcoded to ETAAPP.