Goal:
How To Add/Update Amazon PunchOut Payment Method
Steps:
Go to Settings → Integrations (under Tools)
Next to PunchOut, select the View button
Click on ... → Edit Group
Click Add Credit Card Account
Fill in the information and click Save
Now select the Credit Card from the dropdown and click Save Changes
Additional Information:
If a Credit Card is selected as the payment method, the items will appear in Credit Card Reconciliation
If "Other" is selected, it will appear in your unbilled items to add to a bill.