Pdfcrowd Dev Team

Please check if your php.ini allows opening URL by
allow_url_fopen = On
or
allow_url_fopen = 1

https://www.php.net/manual/en/filesystem.configuration.php

Also check WordPress debug log for errors:
https://www.wpsecurityauditlog.com/wordpress-admin/enabling-wordpress-debug/

Are you using some shortcode options?

Is the simple test working?
<h2>Test Pdfcrowd</h2>
[save_as_pdf_pdfcrowd]