Sync SharePoint task list to iPhone (iOS)

I have previously been able to synchronise a SharePoint site task list to my Reminders on my iPhone. The last time I did this was a long time ago and I think it was using a previous version on SharePoint 2013.

 

When I look at the 2 different task lists (old working one and new one not syncing to iPhone) in Outlook (PC Client) the properties for both task lists are different. See screenshots.

 

To me it looks like something has changes architecturally in SharePoint between 2013 to 2016.

 

Can someone tell me if they have this working and how to do it.

 

Thanks, Ross