This issue is most often caused by a mismatch between the SmartThings region and Konnected Cloud region. These must be in the same region, otherwise ST cannot send commands to Konnected.
Check your SmartThings location country/region by logging in to your Samsung account at Samsung account.
Check your Konnected account region in the Konnected app > My Account.
If you change the Konnected account region, in order for it to take effect you will have to re-sync the settings to each of your devices by going to Manage Zones > Sync to Device.