Statistics key &1 not permissible here!

What causes this issue?

Certain rules apply for the assignment of statistics keys:
Interest documents 'G'
Dunning charges 'G'
Downpayment requests 'A'

System Response

Processing is canceled because the statistics key you have specified
does not correspond to these rules.

How to fix this error?

Change the statistics key accordingly.

Error message extract from SAP system. Copyright SAP SE.