No function module available with activity &1

What causes this issue?

The dunning activity called is assigned to a function module 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.

Procedure for System Administrators

Check and/or change the system settings. You have the following
options:
Delete the activity from the dunning level called in the current
dunning procedure.
Define an existing function module for the dunning activity called.
INCLUDE FICA_NA_F5 OBJECT DOKU ID TX

Error message extract from SAP system. Copyright SAP SE.