Functional location & does not exist

What causes this issue?

You entered a number for a functional location that does not exist in
the system.

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?

Check your entry. If you entered the wrong number by mistake, overtype
the field with the correct number. If you do not know the correct
number, select the desired functional location using the possible
entries function.

Error message extract from SAP system. Copyright SAP SE.