I’m surprised to see an established manufacturer use plastic gears to drive the opening and closing of a garage door. In time, the plastic gears wear and the garage door opener cannot perform its duty. You can see the worn threads around the rim of the gear, and even worse, which is the cause for slippage, is the worn and cracked area around where the shaft goes. The square shaft no longer is secure inside of the gear and thus it slips while trying to open the garage door. Fortunately, this is easily (and cheaply) fixed.
For my garage door opener, Genie model GCG350, the outer housing is removed with a single screw in the middle of the case. With the housing removed, there are three screws that need to be removed from a plastic, black enclosure that houses the gear. With the gear housing removed, the gear is easily removed, along with the square, metal shaft. Be careful when removing the gear housing as there are two metal washers around the shaft and laying on top of the gear housing that can easily fall off. If the gear does not come off with very little effort, pull the cord on the chain drive and adjust the garage door such that there is no more tension on the gear. Replace the gear with a new one; I ordered mine from garagedooropeners on eBay, Genie 27096A Garage Opener Drive Gear, for $2.71 + $3.75 shipping (order more than one as this repair only lasts a few years). Add everything back in reverse and it should work fine. It is a bit tricky to get the gear casing on as it is difficult to line up the shaft and keep the washers in place – it just takes a bit of patience and very little effort.