A lot of things can change in two years, and smartthings has gone through a massive architecture change in that time. So things may not work quite the same way, but the basic principle is sound.
First, just to be sure, did you buy an “ecolink” sensor with dry contacts? Or did you buy an “ecobee” sensor (which won’t work for this purpose).
First rule of home automation: “the model number matters.“
Anyway, to find currently available devices that have dry contacts, see the community FAQ on that topic:
FAQ: List of devices with dry contact input from external sources
Normally a device which offers dry contacts will include wiring instructions in its own user manual. 