If the Service Order specifies that payment will occur by a method other than a credit card, Subscriber will provide a purchase order number in the applicable amount (or reasonable alternative proof of Subscriber’s ability to pay the fees specified in a Service Order), and promptly notify Fastly of any changes necessary for payment of an invoice. Fastly will invoice Subscriber either monthly or according to the billing frequency stated in the Service Order. Invoices to be paid by credit card are due on the invoice date, all other invoices are due net 30 days from the invoice date.