Can anyone provide me with some guidance in configuring SOTI Hub pls?

Running MobiControl Version: 14.4.2.1307  with SOTI Hub App Version 14.3.0 Build 24 on Android.

I'm trying to connect to our internal SharePoint 2016 On-prem content. My repositories appear as folders but I can only see the mandatory fetched files, which I can't download and I keep getting 'the corresponding repository is not authenticated' messages. 

Having exhausted all the documentation I can find, I feel I have everything set up correctly but when I run SOTI Hub I get the following ( my steps in this order):

Launch SOTI Hub

Logging in...

Message: Mandatory file sync failed. View event log for details

App loads showing greyed out Collated Data Folder & My Files | Select Collated Data

Select Collated Data 

Message: Logging in

Folders for each repository alias appear.

Select a folder

Message: Alert. The corresponding repository is not authenticated. Please login

Click OK - Loading

Can view mandatory files - select  a file

Message: Alert. The corresponding repository is not authenticated. Please login.

Click OK - loading

filename downloading failed.

Event log shows: Unable to connect to repository 'repo name'

The content repositories in my SOTI Hub configuration are set with credentials with full access to SharePoint and as I can navigate into the repositories and see the fetched files I'm assuming the authentication issue isn't with the content repository configuration settings. 

I'm therefore wondering if it's to do with SharePoint being internal and not published to the web. I've installed ERG to see if this will route the requests successfully but when I select use Enterprise Resource Gateway and my ERG I get the same errors. When I check my ERG via the MobiControl web console there's nothing in the log window so I'm guessing this isn't configured correctly.

I've run out of ideas so if anyone has successfully managed what I'm trying I'd be extremely grateful for some assistance.

Many thanks