Payment forms are common these days, and Drupal has already many out-of-the-box modules to implement a web shop.
But these modules are often very cumbersome, complicated, and not-so-easy to tweak for your own needs.
So, let’s (re)start from the beginning: let’s implement our own Payment form with Payment, and throw Ubercart, Commerce, and all his friends away.
Note that the use of Payment is compatible with Ubercart and Commerce, but please let me make it simpler.