My understanding is that you can't grow amanita muscaria indoors. It grows alongside the live roots of birch trees and oak trees.
It needs the roots to give it certain nutrients. I made up some spore water a few years ago and sprinkled the water around in a piece of woodland where there is lots of silver birch, but it seems no mushrooms grew there from that spore water as far as I could tell.
I think amanita muscaria is just one of those mushrooms that you have to find growing wild, just like liberty cap mushrooms (psilocybe semilanceata). There are a few types of psilocybin mushrooms that you can quite easily get spores for online, that grow easily enough indoors, but you have to keep everything very clean and sterile until the grow medium is fully colonised.