We invoice all customers on a monthly cycle, ideally the invoice would be created 7 days before the due date so that their direct debit would be triggered and payment is received on the due date. However if the due date is the 1st (or any date between the 1st and 6th) there is no way I can see to create the invoice 7 days before this.
There isn’t an automated way of doing it for the 1st of the month unfortunately. You could generate the invoices around, for example, 25th of the month and then manually trigger the direct debits on these invoices. This can be done in bulk too.