Need help tracking down an error

I forked invoiceplane.
I made some changes to the mpdf helper. Basically my goal is when an invoice is marked as sent the server automatically prints it. Currently the way I changed the code, I expect it to attempt to send a print job when I click the download pdf button. I was getting server error 500. Now I just get a white page. The logs folder is empty and apache’s log is empty, even after configuring php.ini to log every error. I don’t have much experience with php. I’m confused what to do next.

Set the log_threshold to 2 in the config file.

Since the app is working under CI you can always put it in development mode and it will write all the errors on screen have fun and i hope it helps cheers!!!