The Test Source URL button in the External Dynamic Lists (EDL) popup window of the Palo Alto Networks Firewall gives a URL access error.
Palo Alto Networks is aware of this issue for the 8.1 code, and it is documented in the PAN-OS Release Notes, version 8.1.8: https://docs.paloaltonetworks.com/content/dam/techdocs/en_US/pdf/pan-os/8-1/pan-os-release-notes/pan-os-release-notes.pdf
Currently there is no fix for this, but Palo Alto Networks is working on one.
When viewing an external dynamic list that requires client authentication and
you Test Source URL, the firewall fails to indicate whether it can reach the
external dynamic list server and returns a URL access error (Objects > External