Set up the store first
Then bring the game over from CrossOver.
What happened
To bring a game over from CrossOver or Recall, Malbec puts it in Malbec’s own copy of the game’s store, and that store isn’t set up yet.
The fix
Click Set Up the Store, then bring the game over again.
When to write to us
If setting up the store shows a different message, its page explains that one.
Email support@malbec.app. For a diagnostics file, choose Help › Export Diagnostics… in Malbec and attach the zip it saves. It has no account details, and your home folder is masked.