How can I send the path_body to update quantities via the SP API of Amazon Seller Central in Python?

For example, I have this code:

request_params = {
    "MarketplaceIds": marketplace_id,  # required parameter
    "CreatedAfter": (
        datetime.datetime.now() - datetime.timedelta(days=60)
    ).isoformat(),  # orders created since 30 days ago, the date needs to be in the ISO format
}

#UPDATE QTA
def update_inventory():
    url = "https://sellingpartnerapi-eu.amazon.com/listings/2021-08-01/items/XXXXXXXX/1AAA-3333-VVVV"
    
    headers = {
        "x-amz-access-token": access_token,  
        "Content-Type": "application/json",
        "x-amz-date": datetime.datetime.utcnow().strftime("%Y%m%dT%H%M%SZ"),
        "Host": "sellingpartnerapi-eu.amazon.com",
        "x-amz-marketplace-id": marketplace_id,  # My marketplace ID
    }

    patch_body = {
        "marketplaceIds": "APJ6JRA9NG5V4",
        "patches": [
            {
                "op": "replace",
                "path": "/attributes/fulfillment_availability",
                "value": [
                    {
                        "quantity": 1,
                        "fulfillment_channel_code": "DEFAULT",
                    }
                ]
            }
        ]
    }
    
    response = requests.patch(url, headers=headers, data=json.dumps(patch_body))

    return response.json()

In the PATCH operation, what am I doing wrong?

I’m getting an InvalidInput error, and I’m unsure how to create calls to update data, while I have no issues with regular GET requests.