I'm not sure how far you've gotten with Smartthings custom apps so apologies is this is too simplistic.
Are you using the classic or the new Samsung App? Below are simplistic directions for the classic app.
- You have to login to their IDE at http://graph.api.smartthings.com. This is very much like Hubitat's "Apps Code" and "Drivers Code" sections.
- After that, you goto the "My SmartApps" section in Smartthings IDE and pull in the Smartthings specific groovy code the same as you did for the Hubitat groovy code in the "Apps Code" section of Hubitat.
- After that, you goto the Smartthings classic mobile app, automation bottom tab, SmartApps top tab, scroll to the bottom and select "Add a SmartApp".
- Scroll to the bottom of the "add a SmartApp" window and select "My Apps". This will pull from your custom applications installed via the IDE (the one you just installed).
- Choose the "HubConnect Remote Client" and follow the directions from there.