The Issue #
If you are on WP Engine and using the Gravity Forms User Registration Add-on to create a registration form and the link that is sent via email to set the password keeps throwing the “invalid key” error, try the following instructions.
The Solution #
Disabling Object Cache fixes the issue. This is done on WP Engine User Portal > Caching > Object Cache > Disable.
I contacted WP Engine to disable this cache only on wp-login.php (the script where the error occurs) but that script is already excluded from cache: https://wpengine.com/support/cache/#Cache_Exclusions
So, the unique solution for this is to Disable Object cache for the whole site.
Additional Information #
My theory of Toolset being the cause of the issue was because the links started working when I disabled Toolset, but now I understand that it was because the cache was automatically purged when the plugin was disabled. And I blamed that plugin because it has code related to the “reset password” feature that is the same that uses Gravity Forms User Registration Add-on to set the password of the new user.
——-
Lauren asked me if just purging the cache wouldn’t work. That’s not a solution because the cache will be purged and it will work for a moment, but then the data will be cached again and it will stop working again.
——
Why we didn’t have this issue before? I have 2 theories:
We never tested this exact workflow: creating a new user with Gravity Forms User Registration Add-on.
We never tested this exact workflow with the plugin updated to version 5.0 (that version has a big change on how the temporary key is generated).
