The point of the test is to make sure that PayPal enrolments still work (anti-regression test). Preparing the testing environment: Test site with a public URL (ngrok may help) PayPal account Put $CFG->usepaypalsandbox = 1; into the site's config.php Prepare three separate browser sessions so that you can be logged in as a different user in each of them. Test Browser 1 In the first browser session, log in to https://developer.paypal.com/developer/accounts/ to get the seller (facilitator) and the buyer sandbox account credentials. You may have to set the passwords for these accounts by expanding the email column, clicking on " Profile " and clicking on " Change password "  Log in to Moodle, enable and configure the PayPal enrolments. Use the sandbox seller's emails as the "PayPal business email" Create a course. Go to Participants Click on the cog menu and select " Enrolment methods ". Add the Paypal enrolment method. Browser 2 In the second browser session, log in to https://www.sandbox.paypal.com as the seller Go to " Profile > Profile and settings > My selling tools > More selling tools > PayPal button language encoding " Make sure you have your website's language set to " Western European Languages " Click the " More Options " button Set encoding to " UTF-8 " and let the same encoding be used for IPN, too. Go to " Profile > Profile and settings > My selling tools > Getting paid and managing my risk > Instant payment notifications > Update " Turn IPN on and set the notification URL to your site's " enrol/paypal/ipn.php " (e.g. " http://[URL_TO_YOUR_MOODLE]/enrol/paypal/ipn.php ") Go to " Profile > Profile and settings > My selling tools > Getting paid and managing my risk > Block payments > Update " Set " Allow payments sent to me in a currency I do not hold " to Yes. Browser 3 Before starting this, you may want to watch your Moodle's access log for incoming POST requests for enrol/paypal/ipn.php (so that you know when PayPal sends the payment verification). For example: tail -f /var/log/apache2/error.log In the third browser session, log in to your site as a student. Attempt to enrol in the course via PayPal When asked to log in to PayPal, log in as the sandbox buyer. Pay for the course via PayPal TEST : Confirm that the user is enrolled into the course ( Note it may take some seconds or a minute for PayPal to send us the IPN, upon which we enrol the user). CHECK : You Moodle's error log does not contain any PHP notices or Moodle warnings related to the ipn.php file Notes and tips When logged in as the seller into the paypal sandbox, there is an IPN history report available at the Classic view Activity