SD-RED 20 3G/4G expansion module not working?

Question

Hi, 
 I am trying to configure a new SD-RED 20 with a 3G/4G module. 
 I have provisioned the RED successfully using the WAN port, and i have enabled 3G/UMTS failover with the appropriate settings, now when i disconnect the WAN, the tunnel drops. I don't know if i am missing something or if the module is faulty... 0_o 
 Has anyone had similar issues or success with the 3G/4G Expansion Module? Especially on the Telstra network? 
 Thanks in advance, 
 Taison

Taison Eady · Accepted Answer

So I have made some progress on this issue, and i thought i would share in case anyone else has the problem. Sophos support has not contacted me during any of the several arranged time slots since i first had this issue, so was on my own with this one. 
 
 To use the 3G/4G expansion module to connect, i had to add an initialisation string in the APN field when configuring the RED as suggested in this similar answer: 
 https://community.sophos.com/products/xg-firewall/f/firewall-and-policies/116521/4g-telstra-dongle-huawei-e8372-and-disabling-nat 
 
 So the full APN ended up being: telstra.extranet AT+CGDCONT=1,"IP","telstra.extranet" 
 And Dial String: *99# 
 
 It seems to be working now despite all the status lights flashing green, except the system light which is flashing red.