Open Source: https://github.com/xfrocks/bdPaygates
1. Replace built-in PayPal with compatible implementation (no change needed to your system)
2. Support other pay gates as additional download.
3. Support paid resource (in XenForo Resource Manager)
1. Upload the library directory into your XenForo's
2. Import the add-on
3. Configure pay gate options in User Upgrade page (AdminCP)