Never mind, worked immediately after sending this mail ;-)

On Mon, Aug 22, 2016 at 8:37 PM Magnus Manske <magnusmanske@googlemail.com> wrote:
I am trying to create new items by supplying a large-ish JSON structure, but I keep getting "The serialization is invalid". Sadly, that does not tell me which part is invalid.

Can anyone see what's wrong? (I suspect the references, but I don't want to create unreferenced testing items, and test.wikidata.org has different properties apparently...)

https://tools.wmflabs.org/paste/view/7b2aab11

Cheers,
Magnus