Can you try a curl from the message processor terminal? If it's working check with all message processors. If all look good then something need to be configured in proxy. If it's not working then involve your network team to find out where is the blo...

This by default goes from the rest client. Can you try the curl request from a terminal instead of postman/soap UI?

yes, you can do. But, take care of copyright things when you use any resource from other resources.