Could not find a valid session key appearing on Paypal transactions
Overview
We are experiencing a problem similar to that reported in #1997 (closed) , except we're using Civi 5.35.2 and Drupal 7.80. When returning from Paypal after a contribution payment (user presses the "Return to seller" button), the "Could not find a valid session key" error appears. The transaction is completed successfully in both Paypal and CiviCRM. The only problem is that the thank you page is not displayed appropriately.
Reproduction steps
- Complete a donation page using PayPal Standard
- Click continue
- Go To PayPal
- Make payment
- In Paypal, press the "Return to seller" button
Current behaviour
Error appears as described
Expected behaviour
Thank you page should be displayed to user
Environment information
- Browser: Chrome 91.0.4472.77
- CiviCRM: 5.35.2
-
PHP: 7.3.28-1+0
20210503.84+debian91.gbp6819da - CMS: Drupal 7.80
- Database: MariaDB 10.4.13