Suggestion received from Glen Robson @ Enigma Interactive on 23 Nov 2020:
"If we want to link the push notification with a message (by sending both in the same request) do we need to supply a URL? I assume the url is what is used when the notification is clicked and if we send the data for both a push notification and a message would we really need to send that URL?"
If sending a communication by both channels (in-app message and push notification), it is a reasonable expectation that the action of the push notification should default to opening the app messaging inbox within the application. This should be the default behaviour if the API consumer leaves the optional URL null on the request.