When configuring and testing a Slack Plugin notification alert within VMware Aria v8.14.1 (22798986), I receive an error on the Validate Notification Configuration process, specifically on the second step of "Establish Endpoint Connection," seemingly stating that my Slack Webhook URL is "Name or service not known."
However, if I SSH to the vROPs/Aria VM and execute the same POST command against the same webhook URL using the same JSON data, the command works and I see the Alert Notification populate on my Slack Channel. The only difference, as far as I know, is that one test is through the Aria Web UI, and the other test is through the Photon OS command line -- otherwise, all the data (JSON payload, proxy server settings, everything) is exactly the same.
What could I be missing that would make the web UI validation test fail, but allow the command line (as root) to successfully POST?