Three digital phone which accept incoming calls on a ddi route are diverting after 6 rings to one of the 3 prime numbers, display on diverted call phone states incoming number label and "CFNA". All three phone have all their forwarding functions (EHT,FDN etc) set to the their own prime number (key 0 scr appearance). Two of the phones are the main answering point, the third is a backup answer, every incoming call rings on one the main phones and the backup phone. (They have the same numbers programmed in the scr keys)
The six rings makes sense as that is programmed for cfno, however I can't work out how they are forwarding to the backup.
Probably missing something obvious!!