Dear Pritesh,
In this case you need to substitute the field "fixed days" in payment term box in OBB8 on the basis of last billing day of previous.
I.e. Day of last billing date -1
You can try to capture that date from the VBRP or VBRK table.
You need to specify the additional month as 1 as given in my prevoius comment.
BR,
Sapan
