title: How to debug php scripts at server side? In a situation client page doesn't show response
body: <p>I'm currently testing a script on my host. This script is to accept PayPal IPN data, do a couple of things (ie. data verification), send necessary data to a specific email address, and more.</p>
  
  <p>I'm using a test tool on the PayPal site to post test data to my script. My script doesn't work: there should be a code issued but I can't see the error. The test tool in PayPal just does the post and doesn't seem to accept any response. I want to see what happened in my script so that I can fix it. How can I get error messages my script outputs?</p>
  
  <p>Any ideas?</p>