UnityWebRequest never returning from yield return www.Get() on Android and iOS when backend is IL2CP

I'm fairly new to networking so there's chance (hopefully) this'll be an easy question. I've set up an apache server that's reached via an HTTP request e.g. http://myserver.ddns.net. This method below reaches the yield statement but never proceeds. What's weird is that it works in the editor and if I deploy to android using the Mono backend, however doesn't work when built with IL2CPP on either android or iOS (unsure about iOS using Mono). My instincts are using http isn't allowed (need https?) and / or I should use a different framework like WWWRequest or HttpRequest instead?

Any thoughts would be greatly appreciated as this is app breaking at the moment! Thanks

Code (CSharp):

1.  
2. private IEnumerator GetEventsRoutine(Action<bool, StoredEventData> callback, bool forceGet)
3. {
4. LogUtil.Write("Trying to get new event data");
5.  
6. // get last update time
7.  
8. DateTime lastUpdated;
9.  
10. if (!forceGet)
11. {
12. string lastUpdatedString = PlayerPrefs.GetString(m_lastUpdatePrefsKeys, new DateTime(0).ToString());
13.  
14. lastUpdated = DateTime.Parse(lastUpdatedString);
15. }
16. else
17. {
18. // this will make the server skip the update test and return events
19. lastUpdated = new DateTime(0);
20. }
21.  
22. WWWForm form = new WWWForm();
23. form.AddField("date", lastUpdated.ConvertToUnixTime().ToString());
24.  
25. UnityWebRequest www = UnityWebRequest.Get(m_url);
26.  
27. yield return www.SendWebRequest();
28.  
29. if (www.isNetworkError || www.isHttpError)
30. {
31. callback?.Invoke(false, default);
32. LogUtil.WriteError(www.error);
33. yield break;
34. }
35.  
36. LogUtil.Write("Got new event data");
37. }
38.