Roundcube webmail is not able to work when LiteSpeed is installed in Plesk: Unsupported PHP version. Required PHP >= 7.3

Symptoms

• Roundcube is not able to load, reporting that PHP version is not supported:
  Required PHP >= 7.3

• LiteSpeed is used instead of Apache

• Attempts to switch the version of PHP for Roundcube using the How to change PHP version for webmail in Plesk for Linux
  article has no effect.

• PHP Selector is used

Cause

• In some scenarios LiteSpeed ignores Plesk PHP settings for webmail and uses bundled LSPHP. Since it is LSPHP 5.6 Roundcube is not able to work.

Resolution

Replace the LSPHP 5.6 binary with a symlink pointing to the more recent version of LSPHP:

1. Backup default lsphp binary:

# mv /usr/local/bin/lsphp /usr/local/bin/lsphp-bk

2. Create a symlink to LSPHP 7.3 or other version installed on the server:

# ln -s /opt/plesk/php/7.3/bin/lsphp /usr/local/bin/lsphp

Additional Information:

For reference: LiteSpeed Troubleshooting guide