Prefix "&1" has been used for the process; use the same prefix

What causes this issue?

You are trying to generate steps for a process, but the steps for this
process have been generated before, therefore the process authority
object has already been defined.
You see this message because the prefix for authority object that you
enter differs from the existing authority object prefix.

System Response

The system combines the prefix and the process ID to create the
authority object for this process. Only users with roles assigned to the
authority object have access to this process.
Therefore, the system gives the error message if you are trying to
generate a second authority object for the same process.

How to fix this error?

Do one of the following:
Use the existing prefix to generate steps for the process, if a new
process template is assigned to the process during the specified period.
Delete the existing steps and then generate steps for the process using
the new prefix.
In this case, you must use transaction SU01 to grant authorization for
the new authority object to users.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.