Failing To Create Api Order Using Produts From Multiple Vendors

Hi, everything is in the title.

I would like to create an order using API, but somehow i can't submit more than 1 vendor's product. Here is my last test trying to :

"notes": "test api",
"shipping_ids":{"1022221111": "20","1022221112": "20"},

I was trying to use product_groups to link proper shipping id to grouped products (grouped by vendor of course) but only the first product is shown in the created order.

Any idea is welcome since the doc is not clear at all on this point.