This message means that the app is unable to resolve a domain to an IP address.
Ask the user to look up the domain using dnslookup. For example, at the command prompt type your equivalent of the below to see whether the expected IP address and port are displayed.
nslookup -type=srv _xmpp-client._tcp.example.com
Here is an example:
If there are multiple records, the one with the lowest priority and highest weight is selected first.
Resolve the issue with the IT team in your organization.