Basically, a few moths ago I made installation thing in the new launcher for beta 1.0, and I have not yet been able to get it to work. I went more into depth here: https://www.reddit.com/r/Minecraft/comments/er119q/i_need_help_playing_older_versions_of_minecraft/
Can we have more info than "it's not working"?
The top of the error pop-up said "Failed to download file, the file contents differ from what was expected."
Hope that helps.
And can we have the entire error message, not just "the top"?