This is the error message you will receive from our API if you don't have a valid payment method:

"errors": [
"status": "400",
"title": "Payment Method Missing",
"source": {
"pointer": "Your previously submitted quote has been invalidated."
 "detail": "A valid payment method is missing"

Also, if youdon't have a valid payment method, this message will appear on the the cart page:

If you get this error, then the company administrator should log into and go to Settings & Data -> Payment Methods (

The screen will look like this:

Once you add a Credit Card, Bank Account, or PayPal account, a validation check will be run.  Assuming it passes that, then the method will move from being "unvalidated" to validated".  You will receive an email confirmation that the card has been approved: 

Customers can also place multiple payment methods and reorder them in priority order of how they'd like to be charged/used.