The answer according to the spec page is: "Micro SD card memory, IP67, PoE". In the details of the PDF it says: "Mirco SD card 128G", no mention if this is a maximum, or the card included in the camera. Even if they intend it to be read as 'maximum', in my experience many companies do not update their documentation frequently, and at the time of publication 128GB might have been the biggest card available.
So, all-in-all, I'd like to have a word from the vendor or a user to know if 256GB will work before plonking down the money for a card I might not be able to use.