Error presents itself as follows:
This is due to a communication error between the gateway and the 3rd party URL service.
A "curl -v -k https://external.domain.com/path/to/remote/service" from the gateway will show that we receive errors when trying to communicate to this 3rd party service.
These errors are network, not gateway related. They are most likely a firewall issue. We recommend speaking with your networking team to resolve.