You should post the relevant lines from your php error log, to find out whatโs the cause exactly.
One very common reason is because the php CLI (command line environment) - which is what this cron line in fact is interacting through - is running with possibly different environment/settings, missing some necessary linux security permissons/ownership, compared to the php web environment/settings (typically php-cgi or php-fgci).
But you should post your php error log lines just to see exactly whatโs the reason for the error.