How to pass codeigniter's CSRF token to Paypal Express Checkout?

return paypal.request({    method: 'post',    url: CREATE_PAYMENT_URL,    headers: {        'x-csrf-token': CSRF_TOKEN    }}).then(function(data) {    return data.id;});

You should be able to resolve this by adding the X-CSRF-TOKEN parameter to your http headers for ajax requests. Assuming you are utilizing jquery, the below should resolve the issue:

$(document).ready(function(){    $.ajaxSetup({        headers: {            'X-CSRF-TOKEN': '{{PUT_YOU_CSRF_VARIABLE_HERE}}'        }    });    var CREATE_PAYMENT_URL  = 'https://#######/paypal/create';    var EXECUTE_PAYMENT_URL = 'https://######/paypal/execute';    paypal.Button.render({        env: 'production', // Or 'sandbox'        commit: true, // Show a 'Pay Now' button        payment: function() {            return paypal.request.post(CREATE_PAYMENT_URL).then(function(data) {                return data.id;            });        },        onAuthorize: function(data) {            return paypal.request.post(EXECUTE_PAYMENT_URL, {                paymentID: data.paymentID,                payerID:   data.payerID            }).then(function() {                // The payment is complete!                // You can now show a confirmation message to the customer            });        }    }, '#paypal-button');});