mPDF not rendering images (mPDF error: IMAGE Error Could not find image file)

Question

We are getting plagued with this which started in April on working server. Everything was fine with our application until the customer reported that PDFs were no longer dis

Answer 1

With same issue, I found that get_headers() returns:

"HTTP/1.1 412 Precondition Failed"

Provider says this was due to web firewall, because the request was badly formed and the user_agent not set.

An ini_set('user_agent', 'Mozilla/5.0'); solved the problem.

In a WordPress plugin using mpdf, mpdf doesn't use WordPress http classes and doesn't set user_agent. I solved this by adding in mu-plugins:

global $wp_version;

ini_set('user_agent',apply_filters( 'http_headers_useragent', 'WordPress/' . $wp_version . '; ' . get_bloginfo( 'url' ) ));