Support for Customer Notes in Checkout API

The current POST/Checkout Mail-In Offer endpoint, lacks a field for capturing user-provided notes. We need to extend the API schema to allow customers to include specific instructions, condition reports, or requests at the time of checkout.

Currently, if a user wants to supply a Customer Note they cannot.

• Request Body: Add a new optional field, customer_note (Type: String), to the checkout payload.

• Upload that “Note” as a “Customer Note or Internal Note”.