For AI agents: visit https://documentation.paysimple.com/llms.txt for an index of all pages formatted in Markdown and endpoints in OpenAPI. Append .md to any documentation page URL to get its markdown version.
1. Retrieve the PaySimple Customer Id stored in your system. If you don't have customer ids stored yet, you can call list customers.
2a. If you are using an existing Credit Card or ACH Account, and do not have the Id stored in your system, you can look it up the default card or default ach account for the customer.
