Enable FileMaker Data API access
You must enable the fmrest extended privilege in each database you want to access using the FileMaker Data API. If you don't enable the fmrest extended privilege, REST API applications won't be able to use the FileMaker Data API to access the database even if the database is hosted.
Note For security reasons, enable the fmrest extended privilege only in the privilege sets for accounts that you want to allow access via the FileMaker Data API.
See Editing extended privileges for a privilege set in FileMaker Pro Help.