Learner details

You will need the interest ID which is the cart’s line item’s id we added from Add a line item to a Cart

mutation updateEventLineItem($cartId: ID!, $interestId: ID!) {
    cart {
        updateEventLineItem(input: {
            cartId: $cartId,
            interestId: $interestId,
            quantity: 1,
            learnerDetails: [
                {
                    email: "san+test@administrate.co",
                    firstName: "John",
                    lastName: "Smith",
                    attributes: [
                        # would be {definitionKey: "", value: ""} for any required POS Fields
                    ]
                }
            ]
        }) {
            errors { label value message }
            cart {
                id
            }
        }
    }
}

Will result in:

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