First of all many thanks for your great tutorial example ! It's really great and was exactly what I'm looking for.
I had just a small issue running the code as it seems that the @OneOf directive is not recognized as it seems still under validation so I had to reput :
union EntityResult = | Entity | NotFoundError | NotAllowedError | InvalidInputError | UnknownError
In the code to make it works. Do I miss something to have the @OneOf directive available ?