wkhtmltopdf

On Debian/Ubuntu-based systems you can install it using the following:

$ sudo apt-get install wkhtmltopdf

Although the above should work, sometimes the alpha version of wkhtmltopdf produces better results. You can download and try it.

If you are on a shared host you can require the binaries locally using composer, change the knp_snappy.pdf.binary path in app/config/config.yml to

"%kernel.root_dir%/../vendor/bin/wkhtmltopdf-amd64"

if you required the 64bit one, or

"%kernel.root_dir%/../vendor/bin/wkhtmltopdf-i386"

for the 32bit.

Make sure to clear caches after that:

$ php bin/console cache:clear --env=prod

Then you can upload siwapp to your host.