Maybe it's something to do with this:
Gifting of The Witcher 3: Wild Hunt temporarily unavailable (fix in progress)
Due to a very large number of fraudulent transactions coming in, we have had to disable the gifting option for three items: The Witcher 3: Wild Hunt, The Witcher 3: Wild Hunt Expansion Pass, and The Witcher 3: Wild Hunt - Game + Expansion Pass.
We are working to clarify the problem and prevent further fraudulent transactions from being made.
We will make gifting possible once more as soon as this issue is resolved.
Have you tried asking Judas, or someone else, from GOG staff?