Welcome to the club

!! Although i don't have BT as isp, i can't get rid of NAT errors as well

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Tried same than you did. I can't use tunngle either.
If you use firewall, you can disable it and try again.
Also, you could try to:
- Disable UPnP and use port forwarding.
- Disable Portforwarding and enable UPnP.
- Disable Both.
- Enable both and disable router's firewall.
- Disable both and disable router's firewall.
I've tried that so far (plus UPnP + forwarding) and got no luck. Hope you have more than me

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