set_meta.graphql

mutation MyMutation {
  createOrder(input: {clientMutationId: "123", customerId: 2, lineItems: [{productId: 66, quantity: 1, metaData: {key: "size", value: "XL"}}]}) {
    order {
      id
      lineItems {
        edges {
          node {
            itemId
            orderId
            productId
            quantity
            subtotal
            subtotalTax
            taxClass
            taxStatus
            total
            totalTax
            variationId
            metaData {
              id
              key
              value
            }
          }
        }
      }
    }
  }
}