One relatively common issue with the PDF reports is when the external URL monitoring cannot be resolved from Pandora FMS Console. We must verify that the URL to customer access, can be solved and accessed from the server where Pandora is installed, for example:
https://monitoring.mydomain.com/pandora
It could be that the server is behind a NAT address and the address which resolves the domain from the local machine is not accessible from the console. To access it you would have to edit the /etc/hosts file as follows:
127.0.0.1 monitoring.mydomain.com