Azure B2C using BankID causing Invalid redirect_uri

Question: I’m trying to implement a test b2C tenant where BankID is used to authenticate the user, but whatever configuration I try with redirect URIs, I’m getting the “Invalid redirect_uri” error.
What makes it worse is that there seems to be no way to figure out why this error occurs, as it is not logged by the Signicat application.
Any help would be greatly appreciated!