Instance & channel_strategy validation

qiskit_ibm_runtime/qiskit_runtime_service.py

@@ -320,11 +320,17 @@ def _validate_channel_strategy(self) -> None:
         instance do not match.
 
         """
+        qctrl_enabled = self._api_client.cloud_instance()
         if self._channel_strategy == "q-ctrl":
-            qctrl_enabled = self._api_client.cloud_instance()
             if not qctrl_enabled:
                 raise IBMNotAuthorizedError(
-                    "This account is not authorized to use ``q-ctrl`` as a channel strategy."
+                    "This account is not authorized to use q-ctrl as a channel strategy."
+                )
+        else:
+            if qctrl_enabled:
+                raise IBMNotAuthorizedError(
+                    "The instance passed in is only compatible with the q-ctrl channel strategy. "
+                    "Please try passing in channel_strategy='q-ctrl'."
                 )
 
     def _discover_cloud_backends(self) -> Dict[str, "ibm_backend.IBMBackend"]:

releasenotes/notes/q-ctrl-instance-check-46181d51f16d18bc.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    If a cloud instance that is `q-ctrl` enabled is used while `q-ctrl` is not 
+    passed in as the `channel_strategy`, an error will be raised.

test/unit/mock/fake_runtime_client.py

@@ -285,6 +285,10 @@ def set_job_classes(self, classes):
             classes = [classes]
         self._job_classes = classes
 
+    def cloud_instance(self):
+        """Return whether or not channel_strategy q-ctrl is enabled."""
+        return False
+
     def set_final_status(self, final_status):
         """Set job status to passed in final status instantly."""
         self._final_status = final_status