Oh! I knew it would be something simple, and it looks so obvious now.
May I suggest a similar example be added to a relevant part of the COPY page in the user manual?
There is nothing in there now to explain that the source folder and file name should be given as separate parameters (and it's a little unintuitive for anyone used to command line copy commands).
Bumping my own old thread... which I know is not great forum etiquette
In my defence, I've just wasted another two hours trying to work out why a simple copy command wasn't working because I forgot that you can't specify a fully qualified target path in the COPY AS command.
And the error message doesn't include any information to indicate that as the cause.
So I'm again suggesting adding a comment or example to the user manual.