I use cube cart 5 for some of my clients stores. In Latin America there is a "PayPal" equivalent called "DineroMail" which is very popular because you can pay in 7 eleven and other convenient stores by printing a bar code.
Dinero Mail has a very usable plugin for version 4 (which is now nonexistent) and you ca see it here (at the bottom of the page) https://mx.dineromail.com/oscommerce
Because this payment module does not work for version 5, I asked the guys at cubecart to upgrade it. They did a pretty good job on it it works like a charm... the only issue it has is that the callback function is not working. That means if someone shops and they buy something... they do get an email confirming payment, but the store admin must manually go to the store and click the ordered as processed.
This is OK if its physical products and maybe I have 1-5 sales per day. but..
If 50 people go and pay a 7 eleven and 15 pay the same product with the same price.. (usually payment is received after 24 hours) I have to manually check each payment and see to whom it belongs. By having the call back fixed, each purchase is marked automatically as paid and if its a digital good, an email will be automatically sent with the purchased download right away.
If the callback is not fix this all has to be done manually.
Cube cart guys asked me if DineroMail supported callback. I said yes because I currently use WHMCS a hosting billing system that has dineromail and automatically marks accounts as paid after 7 eleven stores accept payment.
I attached the latest cuebcart upgraded files that are working pretty good... and also here is the link for the API and IPN
You will find inside those zip files documentation in 3 languages including English.
I will provide you with access to a cubecart 5 installation where you can do tests.