Error testing connection to IDCS REST APIs with OAuth User Assertion Authentication type

Testing a service connection representing an IDCS REST API with OAuth 2 User Assertion Authentication type in the Test tab will not work. In doing so, you will face an error like:

{
"type": "abcs://proxy_problem/oauth/design_allowed_scope",
"title": "Invalid URI",
"detail": "Cannot process \"https://<idcs>.identity.oraclecloud.com/admin/v1/Me\"",
"status": 400,
"o:errorDetails": [
{ "type": "abcs://proxy_problem/auth/scope/update", "title": "Invalid service scope",
      "detail": "Cannot process service scope \"urn:opc:idm:t.user.me\" in IDCS, for URI \"
{1}
\"",
"status": 400
}
]
}

This limitation only exists in the Service Tester (Test tab). Creating a web app and calling the same REST API from the web app works without any issues.