My garage door opener won’t close the garage door and the lights flash.
Check the photo safety devices. (The LED indicators vary with brand of garage door opener.)
On LiftMaster residential garage door openers built within the past 20 years, there is a sender and receiver. These are located at the sides of the track near the floor. There should be a amber LED showing on the sender (always on) and a green LED showing solid on the receiver. If the receiver is off or flashing then something is either blocking the light, or the sender and receiver are not facing each other (aligned).
If the garage door almost completely closes and then reverses, there is probably something hanging from the bottom of the garage door. This can be cobwebs with leaves or perhaps a lifting rope that is blocking the photo safety beam. If there has been flooding, or over zealous washing of the garage, perhaps the photo safety system got wet and these devices should be replaced.