Even with 40 GB free space the launcher means “Not enough disc space” and the patch is failing.
We’re working on various improvements for the launcher, such as more descriptive messages. For now, the launcher needs space free on your C: drive (even if the game is on a different drive), and some users have reported needing at least 45GB free.
Sorry about the trouble, and thanks for your patience.
I did reinstalled the game to circumvent that issue. At least that worked.