We probably need more info, but also there might be things nobody here can support such as network restrictions.
Which specific endpoint are you trying to call?
What security method(s) are you using to connect? How did you implement them in your orchestration/connection/connector?
Are you able to successfully call the REST endpoint from the same network as the Orchestration stack, using a tool like Postman?
The questions to clarify have almost nothing to do with orchestrator itself (yet), but more likely to do with how you're calling, how the calls are secured, and what the network topography is between your machine and the rest endpoint host.
Orchestration REST calls can be tricky but become much easier if we have the postman side figured out in advance.
