Planning to upgrade PHP on our live server tonight from PHP 7.1 (now effectively obsolete)
And I just saw this:
www.php.net/archive/2019.php#2019-08-29-1
Upgrade to PHP 7.3.9 recommended security patch!
Looking through the forums, the latest info I can find is a thread reporting that 7.3.2 is OK for CB.
In CB documentation online, the published CB requirements doc only says php 7.2...