Check numbers cannot have different prefixes

What causes this issue?

A check number can have a part which does not consist of digits, for
example, CH000014. This non-numerical part before the digits is called
the prefix. The prefixes of all check numbers which belong to a
particular bank account must be the same.

How to fix this error?

Check the prefixes of the check numbers entered.

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.