Hi Sahin,
Good day!
Pre-requisite: confirm if the Source is not authoritative in nature or has any active role or LCS to be implemented.
So there are two ways you can try it if the UI doesn’t work:
i. V3 APIs : update-source | SailPoint Developer Community
ii. Visual Studio IDN: SailPoint IdentityNow VS Code Extension Now Available - Announcements - SailPoint Developer Community
Let me know if the either of the two above option helps?
If none of the above works the goto route is to enable debug mode and open the ccg.log on VA and capture any verbose errors.
Thanks,
Aman