Depends on how you installed the extra php versions. I do not know if it is the cause of your problems. But what I would do in your situation is to set the system up as standard ISPConfig on Debian 10, and not mess it with extra installations or version changes. You can try Code: update-alternatives --config php update-alternatives --config php-cgi to get system default PHP back to 7.3, then Roundcube uses that. If this is not possible you would have to do a setup where roundcube is installed in a website and then that website is set up to use the PHP version you want, using ISPConfig additional PHP version mechanism.