You have to go into the Harmony app on your phone, and go to edit devices and link to your SmartThings account. Then it should work for you. Make sure you have the latest updated software on the Hub and your tablet or phone. You may have to force a sync within the application to make sure that the hub is current.
FAQ: About how to setup Harmony on Smartthings
@JDRoberts , did a very good job about explaining how to setup ST with Harmony. Please look this over and see if this resolves your issues.