I'm just about gnawing my limbs off here. I cannot manage to get a ZyXEL P-870H to bridge to a Draytek 2920.

I've upgraded to VDSL2 and replaced my old modem with with ZyXEL. I bought the wifi-less ZyXEL specifically because I already have the Draytek and it's nicely configured for wifi and firewall duties and I figured bridging would be easy (lots of other people here seem to have done it). The Draytek has been bridged to in the past (including with my last preconfigured modem) and never had an issue.

But this time I just cannot manage it, and I have no idea what is wrong. I'm fairly certain I'm making a boneheaded error.

Could somebody please run through some of the basic errors I could have made here? Does anyone else have the same (or at least same brand) setup working?