For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
See Announcement
We have resolved the issue with the J! updater and this will be fixed in the next release.
Posting in the Standard + Professional Support section seems not possible without a subscription, correct me if i am wrong.
Can someone guide me where to find the page where to subscribe and see the subscription prices etc, cant really find it.
Cheers & Thanks