How to upload the main photo for a product in a VK group?

Question

API

I pull the photos.getMarketUploadServer method
Returns:

Array
(
    [upload_url] => https://pu.vk.com/c845123/upload.php?act=do_add&mid=11111&aid=-53&gid=22222&hash=70ec79f43ff0391cc6bec682059cda6b&rhash=acca156f8088f72642ffa8e75f10e6b5&swfupload=1&api=1&market_main_photo=1
)

Further, as I understand it, you need to send it to photos.saveMarketPhoto .
But where to get SERVER and PHOTO? ( didn't understand )

Answer 1

and who will upload the photo?)
the documentation says that you need to send a POST request to this one upload_urlwith the file field containing the file in multipart / form-data format
after successful upload, the server will return an object with fields server, photoandhash