I get a 404 error when I press "Save Changes" in Phrases,
I get a 404 error "Page not found" when I press "Save Changes" in Phrases.
Please tell me how to deal with it.
I tried to invalidation of Plugins, and change a theme.
WordPress: ver 5.5 and 5.8
This could be a plugin conflict. You should disable all plugins and check it. If the issue is solved, activate the disabled plugins one by one and test after each plugin activation to find the conflict maker. Also, please let us know whether your WordPress is a multi-site installation.