def METHOD_NAME(self) -> str:
    instance_arn = self._get_param("InstanceArn")
    max_results = self._get_int_param("MaxResults")
    next_token = self._get_param("NextToken")
    permission_sets, next_token = self.ssoadmin_backend.METHOD_NAME(
        instance_arn=instance_arn, max_results=max_results, next_token=next_token
    )
    permission_set_ids = []
    for permission_set in permission_sets:
        permission_set_ids.append(permission_set.permission_set_arn)
    response = {"PermissionSets": permission_set_ids}
    if next_token:
        response["NextToken"] = next_token
    return json.dumps(response)