@Gort no joy with those settings for me unfortunately. They're the same settings which work fine on my Huawei router. My TP router seems intent on flipping between the 'no sim inserted' error and the...

@Gort thanks for the info. I think CHAP is the only authentication type I haven't yet tried, but I'll give that a shot. Nothing else has worked so far. TP-Link advised me to use PAP so I've stuck to...

@David-TP device details below.

@David-TP APN settings below.

@David-TP additional screen for the mobile settings

@David-TP authentication type is currently set to Pap but I've tried all the other options too. I'm running the latest firmware (1.1.3)