Synology Guest VLAN with UniFi

TL;DR: Tag the guest network as VLAN 1733 in the UniFi Controller.

I have had the Synology RT2600ac for a few years and it was time to upgrade the Wi-fi at my work. I used the RT2600ac and bought a new UniFi nanoHD AP. Both are excellent products but making the guest network work properly took more time than I had anticipated.