You have to check the PAyers details inXD02/XD03 if differ from Sold to party.
You can find the Account Assignment group in the Sales Area Data and in the BILLING DOCUMENT TAB
Alternatively you can find the same in the table KNVV-KTGRD and the field is KTGRD
but I've looked in XD02/XD03 multiple times and I can't find the field
It is because, in OBD2, for that Account Group, the said field is set for hidden. Normally, other than Ship To Party, we can see in customer sales area data. Since some clients would like to have this field to be displayed only for selected account group which differs from client to client.