I have no idea what I did wrong.

I ordered three bumble bee toads from Josh's Frogs. They arrived healthy and fat, apparently one female and two males judging by body shape alone. They were small but active and healthy.

I put them in a barebottom QT critter keeper with a small water dish and a the media in which they were shipped as hides, as it was obviously non-toxic and was what I had handy. The QT sits on top of what was intended as their permanent home, so the humidity in their tank (as judged by plant health and hygrometer) should theoretically be about the same as what it was in their QT. It has been around 55-70% humidity in their permanent home since they arrived, with a few dips and jumps here and there.

QT care was as advised - daily misting (I've been doing twice daily as the humidity in my town has dropped considerably since the toads arrived) with ff feedings and regular water changes on their water dish.

What really confuses me is this. The toads have, since I got them last week, been totally fine. They slept in their shipping media, ate like pigs, pooped regularly and what appeared to be healthy (small black rice-like poops). Nothing had changed today except that one of them was spending more time in the water dish than was usual for him. But given that I literally just got them, I wasn't worried about it. Again he was eating and pooping regularly. At approximately 5:30pm all three toads were out and about, hanging around the water dish where they've always spent quite a lot of time. I tapped a few melanogaster into the QT, went out with my friends, and when we came back to my apartment at 9:30, all of the toads were not moving. At 10:30pm my boyfriend finally said he thought there was something up with them, because they all looked "flat". I used their water siphon (aka turkey baster) to gently nudge one of them.

And they are dead. All three of them.

What did I do wrong? I really want to keep these toads, but it seems cruel and pointless if they're just going to die on me two days before I plan to add them to their tank.

I have springtails and isopods arriving for the main tank, probably on Wed or Thurs. I still plan on seeding it, and hopefully getting more toads, but I need to know what went wrong, what I should have done differently.