vsmoraes/laravel-pdf show() function outputting codes on page

When I try to output a .pdf file using vsmoraes/laravel-pdf as below

 $pdf
     ->load($html)
     ->filename($booking->ReservationNumber . ".pdf")
     ->show();

I am getting an output like below:

This happens only in production environment and it's working fine in my local development environment, what could be the issue here?

via Chebli Mohamed