WHMCS PayPal Billing Agreements
We are in need if a custom payment module to create recurring payment agreements using PayPal Billing Agreements with Reference Transactions. This module would be different than the default functionality built into WHMCS which creates a recurring payment profile for a customer. We want to use the PayPal reference transaction tokenization and bill-on-demand features to be able to easily change the payment amount and be able to bill on demand instead of waiting for PayPal to send a fixed payment on PayPal's recurring payment schedule. We have our PP account configured to allow these services.
Essentially, this module would make PayPal's functionality in WHMCS nearly identical to a credit card gateway except that instead of supplying CC info to a gateway, the module would supply the PP ref txn token to make a charge.
Functionality will need to include creating the billing agreement with the customer, and provision to tie into the regular WHMCS hooks for regularly scheduled payments. Rebills that are due on invoices would probably need to run with WHMCS cron daily similar to capturing credit card payments unless there is a better method.
In addition, this module must coexist with the current default PayPal recurring payment scheme in WHMCS and continue to support the current (legacy) payment agreements in place with established customers. So, it will need to work with the WHMCS PayPal IPN processor in a way that IPN notices for the existing (legacy) payments go to the current built in WHMCS module while IPN notices related to the new module are properly passed and processed by the new module.