My geckos died and I dont know what went wrong.

Hey guys. I want to start by saying I own some Gargoyle geckos and have owned a crested gecko in the past. I have fire skinks and have kept snakes and am not new to caring for reptiles in general.I am new to the species I purchased, however. I did some research, and bought some flying geckos online. I made their setup (10 gallon) with a substrate mix of coco husk, coco fiber, charcoal pieces, and sphagnum moss. All the same mix I used with my gargoyles and had success with. I didnt have time to get live plants so I rinsed and used some fake reptile plants bought online. I grabbed some sticks from my yard in a pile that had been clipped from an overgrown tree, washed and baked it as per instructions found online. They had a zoo med 40w moonlite bulb. Temps ranged from 84 F to 68F on the cool side, in the water dish.When the two arrived I was excited. They were so small and cute. I was concerned they shipped with no heat pack, it was hitting right around 50 at night, but they seemed okay. I put them in the enclsure which had been set up for about 4-5 days at this point. One found a hiding spot and stayed there. One explored. I tried to feed them on several occasions and they just never ate for me. On day 6, one passed away. Sad, I contacted the company I bought from. The next day, the other one was dead.The company gave me a bit of runaround for over a week deciding if they'd give me their live arrival guarantee. I took this time to decide what I wanted to do.Maybe they were wild caught young and stressed? Maybe they got too cold in shipping? I don't know but at the end of the week I had bought a 20 gallon crescent enclosure and decided to buy a halmahera gecko. I spent two days setting it up, waterfall along the back, the same substrate mix (not the exact stuff from the other enclosure, new out of the package), purified water from a gallon jug not the tap, and some bark hollows I bought at the pet store. I let it all run for a few days and when they decided to refund me for the flying geckos, I ordered two halmaheras.They arrived on Friday. They were in a box with no heat pack again. Instead of a deli cup they were in a bag stuffed with newspaper, in a Styrofoam cube that was also stuffed with newspaper. That was new to me, but they're bigger. Sure. They were not shy. They wandered around, one peed on me, they ate CGD (same I feed my gargoyles) and drank that night. I turned the light on and they loved sitting in the light. The hottest spot was 86 when I temped it. Coolest was again 68. I went to work today. They wouldn't eat any bugs but happily ate CGD. I got home from work and go to see how they're doing and the larger one is belly up in his enclosure.What have I done wrong? I've reached out again to the company I bought from. I dont know if I did something wrong with the setups but these are the first times this has happened to me over several animals. What do I do with the other one? Do I take it out and put it in a quarantine bin for now just in case?I'm mortified.