TF400856: The following service is not registered in the database: IdentityManagement

I'm running On Premise TFS 2018 Update2, and i'm trying to migrate to TFS online. I'm at the point where i need to make a dacpac of my collection, and in order to do that i need to detach my collection like they outline here:

https://learn.microsoft.com/en-us/tfs/server/admin/move-project-collection?view=vsts#detach-coll

when i try to detach however, i get the error in the title. Any ideas how to get past this? The only thing i've found similar to this issue is at:

https://social.msdn.microsoft.com/Forums/vstudio/en-US/e6ad3a1a-bfe0-44a9-a3e6-3442004c7687/tf400856-error-identity-management-is-not-registered-in-the-database?forum=tfsadmin

which basically says 'uinstall TFS and reinstall it back from backup', which i'd really rather not try if there is an easier way.

Seems the TFS was not completely configured, or something wrong during the running.

Whatever, just as mentioned in the error messages "The following service is not registered in the database: IdentityManagement". It's related to the DB.

So, you can try below things to narrow down the issue:

• Restart the TFS server and the SQL server, then check it again.
• Restore the backup DB, then check it again.

It that still not work, I am afraid you have to uinstall TFS and reinstall it back from backup DB.