Since July 15, 2016, all taxpayers are required to specify the method of payment on their bills, according to the new catalog decreed by the Tax Administration Service (SAT). The new tax receipts should include the code and the description of the method of payment, according to the catalog of SAT

If you apply more than one form of payment, you must register each of the corresponding codes, starting with the one that settles most of the payment and gradually reach the way in which the least amount is settled.

If the payment method is unknown at the moment the bill is issued (CFDI), one may use the expression NA or any other equivalent.