InternalServerError when calling the synchronization API's

I'm looking for a way to automate the process of updating admin credentials inside an enterprise app in AAD. Looking at the Microsoft docs e.g. here this should be possible via the graph api. Whenever I attempt these steps I'm running into "InternalServerError" along with "Microsoft.Graph.ServiceException: Code: UnknownError".

My dotnet code for validating existing credentials is the following.

await graphServiceClient.ServicePrincipals[$"{servicePrincipalId}"].Synchronization.Jobs[$"{jobsId}"]
                .ValidateCredentials(null,null,null,credentials)
                .Request()
                .PostAsync();

The result is the error above with the same error for any other synchonization method. I've considered it could be a permissions issue but I've found that the api does a reasonable job of sending permission issues back so I'm stumped at this point.

Does anybody have any advice on this?