Retrieve a funding source, identified by the given id in the URL.

You can also use the following special keywords (case-insensitive):

• BALANCE retrieves the organization's balance funding source.
• INVOICE retrieves the organization's active commercial invoice funding source.

Note: Commercial invoicing is only available to select Enterprise clients with an existing commercial invoicing setup. If your organization already uses commercial invoicing and you have questions, contact your Customer Success Manager.