I have a Web API deployed on on premise server.
I am trying to call it using Nintex workflow online but it shows error as "Unable to connect to remote server".
Do you see any traffic on your premises server? Any trace of connection in logs? Firewall blocking? Something with your machine? Which action are you using to make a call?
We checked that and we cannot call on premise WEB API from Nintex Workflow Online since server is behind and firewall and ports are block for outside world.
Good and bad to hear that. Maybe you can convince your IT and Security dept. that if you use Azure service bus for communication this will remain secure?