Assign a controller class to the controller &

What causes this issue?

You have not entered a controller class for the controller &V1&.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Implement the controller in an ABAP Objects class. This class must be a
subclass of CL_BSP_CONTROLLER.
Enter this class as a controller class.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.