@bercaakbayir - 2 areas to look at for permissions.

1. Unity Catalog Permission
2. Destination‑level permissions

Please Check,

• UC enabled for your workspace. [Metastore Admin, not workspace Admin]
• CREATE permissions on the target catalog - User or SP should have - CREATE on catalog, USE Schema, Create Table, Write Files (on the external location)
• Ensure fivetran has permission to access the SQL warehouse or cluster it connects to