Test Source URL button in the External Dynamic Lists popup of the Palo Alto Networks Firewall gives a URL access error - Support and Troubleshooting

Test Source URL button in the External Dynamic Lists popup of the Palo Alto Networks Firewall gives a URL access error Issue  The Test Source URL button in the External Dynamic Lists (EDL) popup window of the Palo Alto Networks Firewall gives the URL access error shown below, not due to a SN platform issue:

Cause Palo Alto Networks is aware of this issue for the 8.1 code, which 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

PAN-69505 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 Dynamic Lists).