Hey, NT! Welcome to ST! I just posted my Particle sketch and ST device handler in a new thread. Check it out here.
I don’t know if getting webhooks set up will help you in this scenario. What exactly are you wanting the webhook to do? Mine just refreshes the ST door statuses when it get a state change from the Photon. Like, it just tells my SmartThings DH, “Hey, refresh().” It does nothing else. It may actually be the simplest, most boring webhook ever. WebCoRE even told me something to the effect of, “This doesn’t really do anything. Are you sure this is all you wanted to type?” when I saved the piston.
My setup uses only the Photon for all status and garage door opening functions. The DH is written specifically for that device. I’m not sure how to integrate another device (with it’s own DH) into my DH. I don’t know if it’s even possible. That said, I’m new to coding. I suppose you could have separate devices for the open/close side and the garage door toggling side.