AEP Mobile SDK postback not reaching the specified endpoint on iOS

Hi, I have been trying out the Luma app AEP Mobile SDK tutorial and tried to set-up a postback following the video here https://www.youtube.com/watch?v=r-z9ivQjzOY

For testing purposes, I have set-up a very simple endpoint that I can easily access (tested) from anywhere without any restrictions and it returns the request details in the response. However, when I use it in a postback configured in a Tags mobile property, the endpoint is never called according to the server logs. In Assurance, I can see that a Rules Consequence Event has been triggered and that it carries the correct url in the templateurl property. 

Any idea why this might be? Is there any more configuration required in order to make this work?

I also updated all the extensions to the latest versions.

Any help would be much appreciated.