This following package is based on the Discount Code for osCommerce 2.3.1 Addon.
I was able to reduce the install process from 16 steps down to 9 steps.
Database tables and filenames definition have been removed. I tried to keep the code changes to a minimum.
SQL install/uninstall is done automatically with the ot_ module.
Discount Code 5.1.2. Phoenix
Please apply these fixes also to previous versions.
Older versions, FROZEN, EDGE and Gold BS3, please use Discount_Codes_4.4.3_BS
Fix for wrong order total showing when no tax is applied. Thanks to @bnguru for the report and testing
Added support for stripe sca 3.0 payment module. Thanks to @peterespana for testing
Fixed several minor errors in instructions, ot module and admin page. Thanks to @Demitry