Manufacturers now supply safety sensors with the garage door opener. Installing the sensors as part of the garage door opener installation requires attention to wiring and adjustments to the devices themselves. Garage door sensors and buttons are low voltage (usually 24vdc), and low enough current that for the short runs typical in a garage you don’t need very large cables. Some how the staples may have come out and wire can get caught up in the moving parts on the garage door. Also some sensor wires are run up the wall to where the opener attaches to wall and then run thru the opener rail all the way back to opener.
If your opener flashes twice, then your sensor wire is either shorted or the black and white wires could be reversed. I believe it is an infrared sensor with two wires on each. I have wired them to a 120V plug and the LEDs on them turn on and my motor spins slightly (. Forum discussion: I have Moore O Matic Yellow garage door sensor AAE00298 that is broken. (some call it safety eyes? anyways) Since it’s discontinued, I bought a Digi-Code CR2149 Universal replacement sensor kit.