A website hosted in Plesk shows the warning: Use of undefined constant SOME_CONSTANT - assumed 'SOME_CONSTANT' (this will throw an Error in a future version of PHP)

Symptoms

A website hosted in Plesk shows the following warning:

PLESK_INFO: Warning: Use of undefined constant SOME_CONSTANT - assumed 'SOME_CONSTANT' (this will throw an Error in a future version of PHP) in /var/www/vhosts/example.com/httpdocs/wp-content/themes/houzez-child/functions.php on line 73

Cause

The website is not compatible with the selected PHP version.

Resolution

1. Log in to Plesk.

2. Go to Domains > example.com > PHP Settings and change PHP version to an older one.

3. Apply the changes.