I have followed the instructions to install ghcup on my MacOS by following command:
curl https://get-ghcup.haskell.org -sSf | sh
But I couldn't install it, it prompted errors like these:
Failed to install, consider updating this script via: ghcup upgrade "ghcup --cache install" failed!
stack and ghcup are two different tools.
You can get stack from this website, which involves running the following command:
curl -sSL https://get.haskellstack.org/ | sh
On the other hand, ghcup is a tool that only installs the Haskell compiler (GHC), which means that you won't be able to build a project using Stack. Note that this last installation comes with a build tool called cabal. You can learn the differences between stack and cabal in this other question.
Regarding your error with ghcup, I'd try to use the instructions from https://gitlab.haskell.org/haskell/ghcup. It is the main repo from the project, and probably updated faster. Note that you can use the "simple bootstrap" process, and if that doesn't work, try the manual one.
If you have brew installed, you can use : brew install stack
