Buyer details

You will need:

1. Email address
2. Name (first/last)
3. Company name

mutation updateCart($cartId: ID!) {
    cart {
        updateCart(input: {
            id: $cartId,
            email: "san+test@administrate.co",
            firstName: "John",
            lastName: "Smith",
            company: "Test Company"
        }) {
            errors { label value message }
            cart {
                id
            }
        }
    }
}

Will result in:

{
    "data": {
        "cart": {
            "updateCart": {
                "errors": [],
                "cart": {
                    "id": "T3Bwb3J0dW5pdHk6OTQ4"
                }
            }
        }
    }
}