I am trying to send a kill -10 (SIGUSER1) to a process ID by using a button in a webpage, I have tried different ways to send the signal while passing the PHP variable (which holds the PID) to shell. Below is what I have:

$next = posix_kill($pid3, 10);

Right now, this is giving me the below error:

PHP Warning:  posix_kill() expects parameter 1 to be long, 
              string given in /var/www/parse2.php on line 15

Please advise