I have a client that installed FTTP BT connection last friday with a BT Smarthub 3 . 
They also have a FTTC connection - that works AOK with the Smart VPN into a Draytek 2860 Firmware 3.9.8.4_BT & DSL 576D17_A/B/C HW: A Model Name Vigor2860n System Up Time 51:57:12 DrayTek Mon Jul 28 2025 14:34:29 Firmware Version 3.9.8.4_BT Build Date/Time Dec 16 2024 20:04:44 DSL Version 576D17_A/B/C HW: A
On the new FTTP connection the VPN ( PPTP, SSL VPN tunnel etc) makes the contact and begins to authenticate  but does not authenticate and complete the transaction . 

I have tried to DMZ to a static IP Draytek WAN2 , switched on UPNP , tried Port clamping on & off. 

I have switched off the Firewall on the BT SH3 , and tried port forwarding with it switched on as follows    

PPTP VPN
1723

PPTP VPN gre
47

VPN 50
50

vpn 51
51

vpn 500
500

vpn 4500
4500

vpn 1701
1701

vpn 8443
8443

vpn 443
443

Furthermore , Bridging mode is greyed out on the BT Smarthub 3 

Can anyone help ?