After searching the web up and down for a proper explanation of HA/Hörmann/Shelly how-to, your post finally seems to be the missing link.
Will give it a go and report back.
Any one knows how the schema would like for a promatic4 or is it similar?
First of all. Thanks 
for this missing gem. Was looking for exactly this.
Could anyone correct me if I’m wrong? This setup requires the additional reed sensor to monitor the 4 states. With the built-in you would only be able to detect if the gate is opened or closed right?
Also … wondering the use of the shelly 2.5 …. Or wouldn’t be the best place for the Shelly UNI? Could handle the two reed sensors, powered by 24v and couple of dry contacts to trigger the open/close actions?
I saw some people using shelly 1 plus, but I’m wondering about the UNI. If anyone can enlighten me … 
much appreciated.
Hello everyone, found this thread and it motivated me to finally resolve garage door closing remotely myself 
BUT! ran into kind of an issue, maybe you could help me out?
Got Shelly 2pm, Promatic3 AND, and this is probably the issue JCM Stick30 connected to it for remote (guess so the same system is used everywhere in the house, even for opening entrance door…), guess as cheaper replacement for hormann bisecur. It should be this thingy, connected via board to promatic - JCM Technologies | Stick30
Its connected to pins 5, 21, 20
My issue is, setup everything and it’s working fine - Switch 1 works same as remote basically, Switch 2 shows if the gate is fully open.
But issue comes, when i switch the pin 2 to on position - after that, when I close the garage door by remote, it reopens it. When i put it to off, it works.
I’m now using only shelly app, will be integrating it to Homey later, guess only thing I’m missing is seeing if the garage door is fully locked?
Other than that, everything is connected exactly as in your pics - https://photos.app.goo.gl/nGMZr5PDvnUrV5Cx9
(excuse the wiring, it’s hell, had to move shelly more close to the door to get better signal, so now it’s completely rewired :))
Forget my last question (but might help someone else)… did not properly configure shelly, now it works as it should