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Hey 👋 , Happy end of year 😉 Yeah, there are lots of unfortunate gotchas in

CopySpec

. What you hit is documented, but probably hard to find: You must have one root

into

, then you can configure a child

into

with a block. To be clear, it took me a while to realise this is what you were hitting. See the first note in this section We should for sure improve that error message, to make it much clearer. If you can, please open an issue for it. Related issue

Yup, I'm fine that this is documented, however the error messages are completely misleading