I'm trying to set-up PPTP dial-in from my Moto G5 smartphone (with O2 sim card) to my 2862n.

On the 2862n (Firmware Version 3.9.0_BT) I've enabled PPTP VPN service in 'VPN and Remote Access >> Remote Access Control Setup', and set-up a PPTP dial-in profile in 'VPN and Remote Access >> Remote Dial-in User'.

On the Moto G5, I've configured the stock Android VPN app (in Android 8.1.0) to use PPTP, PPP encryption (MPPE), and entered my username and password.

The problem is that all attempts to dial-in (via O2's mobile internet) fail. There are
no relevant error messages in the 2862's syslog output. The Android VPN app provides no error log.

My 2862n is routable from other draytek routers.

I am stumped as to why the dial-in fails.

Please can you help?