Chamberlain B550 - How to use a relay to open/close door?
Your existing setup will still work even with the new magical control panel that works with 2 wires. A relay wired in parallel that momentarily closes the circuit will activate the garage door. The most likely cause is that your relay is staying closed too long, so adjust it so it's only closing the circuit for 0.2 seconds. You can test a few timing values to find the best one, it might work best as quick as 0.1 seconds or as long as 0.5 seconds.

Test this first by shorting the terminals on the back of your control panel for a split second to verify that this action activates the garage door.

If the test works and the relay still doesn't work, make sure that you wired it in parallel and not in series.