This is not uncommon as these air dams are intended to be easily dislodged. You lost the two pop-off fasteners in the rear. I don't know why Lucid does not provide a couple of them with the car when delivered. I suppose you can get replacement fasteners at any auto parts store. I've tried a few but never found any that fit = I have no idea what they look like, or what the specs are. I had both of mine in the same situation as yours. They will detach when you hit a parking concrete stop or a transition slope like from the street to driveway when the angle too steep. It's no big deal...all these seemingly small aerodynamic tweaks combine to make it one of the slipperiest cars ever built. Fortunately for me the service center is only 10 miles away = had mine replaced at regular service.
In the meantime I used duck tape to hold them up.
Lucid should offer a bag of them on their website, along with the hats and shirts and other swag...or at least show us a picture / give us the specs.
Anyone have a photo of the fasteners ?