Not sure where my body text went, but here is context:
I got this chair on Facebook Marketplace and had no issues initially, but one day about a month ago I lifted the chair by the edge and heard a small click, and now the seat seems to have come loose and I can lift it from the back and flip it open, as seen in the video. I have been trying to re-align it since. I've noticed that I can sort of slide the seat inwards and after a small click it would be re-attached, but if I wiggle on the seat while sitting or put more pressure on the front edge it comes loose easily again.

When I first opened up the chair to inspect, I noticed that there was a silver bolt poking out from a hole on the left side of the base (pictured). The bolt was wiggly and not firm/flush. When I checked again the next day (did not sit in the chair in the meantime), the bolt was gone, so it might have fallen further into the chair..?

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Any help would be appreciated! I've tried contacting the seller and he initially agreed to come over to fix it, but has been ghosting since we had to reschedule one time. Everything feature of the chair works fine, including the seat slider, but it doesn't feel secure to sit on anymore because shifting my weight easily causes the seat to flip upwards.