Formcraft is the best (in my opinion) form plugin for wordpress. I enjoy it much more than GravityForms. You can check the Formcraft 3 Plugin’s page here.
If you are using Formcraft 3 with Wordfence enabled, you will get an error when trying to create or edit a form. This is most likely related to the Wordfence Firewall, which may be blocking some AJAX funcions of Formcraft 3.
The fix is very simple. You must change the Wordfence Firewall status to “Learning Mode“, then go edit and save some forms, then go back to Wordfence firewall and change the status to “Enabled and Protecting” again. That way Wordfence will whitelist the formcraft actions, so you won’t get those errors in the future.