When I close my automatic garage door it closes then a couple seconds later opens on its own

Is there a light sensor near the floor on one side of the door on the inside? There should be a couple of brackets, one on each side of the door. One may have a little light that is on.

When you put your hand in front of the sensor path the light should go off.

Is it constantly on when nothing is in the way? Is it blinking or varying in intensity? Is there something in the way of the sensor, such as cobwebs or leaves?

Sometimes the brackets can get bumped. I've done this. By gently putting pressure on the bracket, moving it slightly forward or back, I've been able to realign the path so the signal is stronger. If its too weak or intermittent the opener may "think" there is an object in the way.

Also, I've had it look OK before in the day, but at night you can see the intensity clearly changing.

Also, can you hold down the button mounted in the garage and close the door? You can sometimes "override" the sensor by holding the button down.

Check you lower limit switch. It should trip when the door is an inch or 2 from the bottom. Once tripped, it defeats the ''reverse when the door hits something'' circuit allowing it to remain closed when it hits the floor. Older doors don't have optical sensors.