Troubleshoot server action

I'm troubleshooting a server action that applies a watermark to a photo. I was getting a 500 error so I went through the steps in the server action and disabled all until I no longer get the error.

Its an action that applies a watermark. I've verified everything and I have other watermarks on the server action that work fine.

How do I turn on debugging to see the details of the action. page debugging doesn't show details.

it worked before but I moved hosting

php, mysql

thanks. I have that set but I get

imagecreatefromstring(): gd-png: libpng warning: iCCP: known incorrect sRGB profile

How do i check php version from old hosted site to new? is that a possibility?