post https://api-test.maast.com/platform/vault/customer//billing
Tokenizes and adds a payment method to a customer profile in Customer Vault. This returns the tokenized card number (or card ID) in the card_id field. You can use this card ID in lieu of the card number in Payment Gateway API requests.
You can add a limitless number of payment methods to a customer profile. By default, the system designates the first payment method added as the primary payment method, and it uses that for subscription payments. Send a 'Set Primary Payment Method' request to change the primary payment method.