PHP clean_all_processes() giving 500 internal error, but still outputs

So my PHP file is meant to check if a variable is null, if so than echo and output, and stop there

Here is that code:

if(is_null($ip)){
  echo "IP is not valid";

  clean_all_processes();
}

So when I try to test this script using the insomnia rest client it outputs the "IP is not valid" but also gives a "500 internal server error"

In my error_log file it spits out this every time

Uncaught Error: Call to undefined function clean_all_processes()

Note: I am using php 7.3 Any help is appreciated!