PHP script will not run bash command

one text

I am having trouble getting my PHP script to run a bash command/script. Here is an export of my PHP script (it is triggered when a HTML form is submitted):

}
chdir('/usr/local/sim/');
shell_exec('killall -9 sim');
shell_exec(./write-sims.sh');
chdir('/var/www/html/');
shell_exec('php -f test.php');
?>

I know that this PHP script is running okay as the 'killall -9 sim' command is executed as expected along with the 'write-sims.sh' script.

I put my bash command inside a PHP script as a test to see if that would work but it doesn't, 'test.php' is as follows:

<?php
shell_exec("find /usr/local/sim/data -maxdepth 1 -type f -name '*.conf' -exec sh -c '/usr/local/sim/build/src/sim --daemon --config {} &' \;");
?>

When I run test.php manually via cli it runs fine however whenever it is called by the first php script it doesn't run.

I have tried switching things around by putting the bash command in a .sh script and calling that from the first php script and also adding the bash command itself inside the first php script but neither work however I don't get any errors in the nginx error log which seems to suggest the script is running okay without errors.

Any idea why this is not running but runs fine when I do it manually? Thanks!