Invalid method &1 for production campaigns

What causes this issue?

An invalid method was used to access a
<DS:GLOS.355991DD8DAF4C9DE10000009B38F984>production campaign</> via
the <DS:GLOS.E3920C859DC2D3118F370060B03CA38C>APO Core Interface</>.
The operation was terminated.
The following methods are valid:
'I',,Insert,,Insert
'C',,Change,,Change
'D',,Delete,,Delete
' ',,Nope,,No operation

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?

Use a valid method.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.