Contact Form 7 and All in one WP security and firewall
If you unable to submit forms through Contact Form 7 while not logged in (i.e. test in incognito mode) and All in one WP security and firewall is used, make sure that the Disallow unauthorized REST requests is NOT enabled in AIOWP Security and Firewall. (It is mentioned in the yellow info box *hint* *hint*.)
The settings are found in WP Security -> Firewall -> WP REST API tab
I