CASDK-0003: Unable to parse the resource, https:<nnn>. Verify that URL is reachable[...]

Summary:

Hi all,
while implementing a REST Invoke Adapter in OIC Gen 3, configured with "OAuth2 Resource Owner Password Credentials", I'm getting the following error:
CASDK-0003: Unable to parse the resource, https:<nnn>. Verify that URL is reachable, can be parsed and credentials if required are accurate
<nnn>: Name or service not known.

The service invoked is hosted on a public cloud provider, and it's called by OIC through a Connectivity Agent (on-prem) configured with proxy_host too.

Content (please ensure you mask any confidential information):

Testing the adapter results in the above error, when using the Connectivity Agent.
The same error does not occur: