The LifterLMS PayPal WordPress plugin before 1.4.0 does not sanitise and escape some parameters from the payment confirmation page before outputting them back in the page, leading to a Reflected Cross-Site Scripting issue
https://wpscan.com/vulnerability/1f8cb0b9-7447-44db-8d13-292db5b17718
https://make.lifterlms.com/2022/04/04/lifterlms-paypal-version-1-4-0/