Diagnosis
The opener's learn mode wasn't activated correctly, or you're using the wrong type of remote. The Legacy 920 uses Security+ 2.0 rolling code technology.
How to Fix It
On the motor unit, locate the square, colored 'learn' button. Press and release it. The LED next to it will light up solid for 30 seconds. Within that time, press and hold the button on your new remote. The motor unit light will flash once. Release the remote button. Test it.
If That Didn't Work
Erase all remotes and start fresh. Hold down the learn button for 10 seconds until the LED goes out. This clears the memory. Then follow the standard programming steps above for each remote.
Heads Up
If you hold the remote button too close to the motor unit (less than a foot away) during programming, it can fail. Stand 3-5 feet away.