[BUG] [SP-API] [Issue] MLI fulfillment_channel_code parametr

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Feature request
[ X] Documentation issue or request
[ ] Other... Please describe:

I've tried to use MLI mode for my seller account. During manual read I found the value assigned to the fulfillment_channel_code looks different (see examples below). Sometimes it looks like Supply Source name, in other example - as a Supply Source Id. But when I call production API I got AMAZON_NA. It confused me, I don't understand what value should I pass and how to understand return value.

Example from the API doc (https://developer-docs.amazon.com/sp-api/docs/mli-integration-guide)

{
    "productType": "PRODUCT",
    "patches": [
        {
            "op": "replace",
            "path": "/attributes/fulfillment_availability",
            "value": [
                {
                    "fulfillment_channel_code": "StoreID1234567",
                    "quantity": 10
                }
            ]
        }
    ]
}

Same document

{
    "productType": "PRODUCT",
    "patches": [
        {
            "op": "replace",
            "path": "/attributes/fulfillment_availability",
            "value": [
                {
                    "fulfillment_channel_code": "ISPU01",
                    "quantity": 10
                },
                {
                    "fulfillment_channel_code": "ISPU02",
                    "quantity": 10
                }
            ]
        }
    ]
}

Same document, but a little bit lower (also pay attention in camelCase instead of snake_case)

{
"productType": "PRODUCT",
        "Patches": [
        {
            "op": "replace",
            "path": "/attributes/fulfillment_availability",
            "value": [
                {
                    "fulfillmentchannelCode": "353e4e48-6301-4d50-990e-43a86e8787a3",
                    "quantity": 10
                },
                {
                    "fulfillmentchannelCode": "8e07a0c9-ab0a-4108-9f16-83dc3496bee0",
                    "quantity": 5
                },
                {

                    "fulfillmentchannelCode": "DEFAULT",
                    "quantity": 0
                }
            ]
        }
    ]
}

Example from the PROD API endpoint, get listing data (/listings/2021-08-01/items/{sellerId}/{sku}?marketplaceIds={marketplaceIds}&issueLocale={issueLocale})

    "fulfillment_availability": [
      {
        "fulfillment_channel_code": "AMAZON_NA",
        "marketplace_id": "ATVPDKIKX0DER"
      },
      {
        "fulfillment_channel_code": "DEFAULT",
        "quantity": 0,
        "marketplace_id": "ATVPDKIKX0DER"
      }
    ],

SP-API Name and Version or Report/Feed Type

/listings/2021-08-01/items/{sellerId}/{sku}?marketplaceIds={marketplaceIds}&issueLocale={issueLocale}

Expected Behavior

fulfillment_channel_code parameter described (what is it) and unified in the documentation (same value type in all examples)

Current Behavior

fulfillment_channel_code parameter definition is absent in the documentation Examples in the documentation have different type of values Production API returns undescribed value, I can't realise is it bug or not.

Context/Screenshots

I can't integrate MLI in my production

amzn / selling-partner-api-models