order.js

$.ajax({
    type: 'POST',
    url: "https://sandbox-api.didww.com/v3/orders",
    data: JSON.stringify({
        data: {
            type: "orders",
            attributes: {
                allow_back_ordering: false,
                items: [{
                    type: "did_order_items",
                    attributes: {
                        available_did_id: '2ffcad78-ad42-4ae0-ad19-cca48c01d511',
                        sku_id: '7c047af5-3e2f-47f0-a866-8136f8b80e53'
                    }
                }]
            }
        }
    }),
    contentType: 'application/vnd.api+json',
    headers: {
        'Api-Key': 'xxx',
        'Accept': 'application/vnd.api+json'
    },
    success: function (resultData) {

        console.log(resultData);

    },
    error: function (xhr, textStatus, errorThrown) {
        console.log(xhr);
    }
});