SmartThings Device can't be added to a Harmony Activity

I am in my first couple of weeks in working with SmartThings, Harmony, & Alexa. I am having a problem.

SmartThings shows up as a device in Harmony app but when I try to add it as a device to Watch TV or Watch Blu Ray, it does not give me the option to add SmartThings device. Any suggestions? I can assign a light to one of the Home Control buttons. However, I would like to hit Play and have movie start and turn off living room lights. Then, when I hit Pause, pause the movie then turn lights back on to 50%.

Is that doable? Thank you in advance for your help.