Subnumber is not generic (inform system administrator)

What causes this issue?

You called up the function module 'AM_LGJAN_GET' without giving a
generic specification '*' for the subnumber.

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?

Correct the application program.

Error message extract from SAP system. Copyright SAP SE.