Diagnosis
The washer is in a state that blocks remote start. Common reasons: Child Lock is on, the door is physically open, or the cycle was started manually at the unit.
How to Fix It
Go to the washer. Ensure the lid is fully closed. Check the display for the Child Lock symbol. Disable it if present. Start a cycle manually from the control panel, then stop it. Now try starting a cycle remotely via the SmartThings app.
If That Didn't Work
Delete the washer from the SmartThings app. Power cycle the washer. Re-add it to the app as a new device. This clears any software handshake errors.
Heads Up
Remote Start is disabled by default if the washer hasn't been used for a certain period. It's a safety feature. You must be at the machine to enable it again after a long idle time.