Unable to authenticate: problem with Role ARN?

[Loosh64]

I've submitted an issue before; I am now with a different employer and experiencing a different issue. I have installed the utility as directed and created the config file (see --verbose output below), but I am unable to authenticate due to an apparent issue with the Role ARN. Note that I am working in gov-cloud (not the public AWS cloud) and that services are sometimes absent or behave differently. Have you been able to test in the gov-cloud? Does the stack trace below indicate to you what might be wrong? As before, I have redacted certain information in the trace to preserve anonymity.

[me]>pyokta-aws auth --verbose -p rdt-admin
Loading settings from config file "[me]/.pyokta_aws/config"...
Using the following settings...
profile...........: rdt-admin
region............: us-gov-west-1
okta_org..........: [redacted].okta.com
okta_aws_app_url..: https://[okta-org]/home/amazon_aws/0oa46z3dyPZgL5uA24h6/272
aws_role_to_assume: arn:aws:iam::arn:aws-us-gov:iam::[aws-acct-id]:role/AdministratorViaOkta
aws_idp...........: arn:aws:iam::arn:aws-us-gov:iam::[aws-acct-id]:saml-provider/BraxtonOkta
username..........: [email protected]
password..........: <redacted>
sts_duration......: 28800
mfa_choice........: app
config_file.......: [me]/.pyokta_aws/config
verbose...........: True
interactive.......: True
Okta username: [email protected]
Enter Okta mobile app code: [auth-code]
Traceback (most recent call last):
  File "%LOCALAPPDATA%\programs\python\python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "%LOCALAPPDATA%\programs\python\python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "%LOCALAPPDATA%\Programs\Python\Python39\Scripts\pyokta-aws.exe\__main__.py", line 7, in <module>
  File "%LOCALAPPDATA%\programs\python\python39\lib\site-packages\pyokta_aws\__main__.py", line 26, in main
    return dispatch(sys.argv[1:])
  File "%LOCALAPPDATA%\programs\python\python39\lib\site-packages\pyokta_aws\cli.py", line 69, in dispatch
    return main(args.args)
  File "%LOCALAPPDATA%\programs\python\python39\lib\site-packages\pyokta_aws\commands\auth.py", line 99, in main
    return authenticate(auth_settings)
  File "%LOCALAPPDATA%\programs\python\python39\lib\site-packages\pyokta_aws\commands\auth.py", line 71, in authenticate
    resp = aws_auth_with_saml(
  File "%LOCALAPPDATA%\programs\python\python39\lib\site-packages\pyokta_aws\commands\auth.py", line 34, in aws_auth_with_saml
    return client.assume_role_with_saml(**data)
  File "%LOCALAPPDATA%\programs\python\python39\lib\site-packages\botocore\client.py", line 357, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "%LOCALAPPDATA%\programs\python\python39\lib\site-packages\botocore\client.py", line 676, in _make_api_call
    raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the AssumeRoleWithSAML operation: Request ARN is invalid

[me]>

The documentation in the README seems to differ somewhat from the output of pyokta-aws -h, but I have tried numerous variations on the format of the Role ARN without success. Any suggestions will be welcome.