Has anybody made this? I am trying to make a custom payment with external redirect and I have read everything and still can't make it work. Has anybody made a custom payment which requires an external redirection to the bank's page? I have read the paypal workflow and other stuff but if somebody has actually made it (not in theory) , then would be glad to get their help...
Maybe you can start by taking a look at some of these posts: https://www.maxpronko.com/blog/tagayment
Also, you can try to search for payment gateways modules on github. For example, here you can see two options for Argentina: