How to read NamedTtuples with JSON3?

New to Julia
1

I am trying to do the following

using JSON3

struct data
    d::NamedTuple{(:a,:b,:c), Tuple{Symbol,T,T}} where T <: Union{Nothing,Real}
end

JSON3.StructType(::Type{data}) = JSON3.Struct()

But I get an error reading the object

JSON3.read("{\"d\":{\"a\":\"n\",\"b\":1,\"c\":1}}", data)
ERROR: UndefVarError: types not defined