Problem with Express Checkout not Redirecting after Successful Payment

[rgolding]

I have been using Express Checkout from PayPal to handle payments on my website. It has been working with no issues. I have now tried to add another PayPal portal for another membership option and have used the same code with small changes but this one does not seem complete the process by redirecting as its instructed. The Payment itself is successful, I can see it in PayPal Activity in both Production and Sandbox, but it does not redirect the page when the payment is complete and i cant figure out why. I have compared the code to the working copy and can see no difference. Below is a snippet of the script (i can post the rest but i thought the rest might not be needed)

payment: function (data, actions) {
                    return actions.payment.create({
                        payment: {
                            transactions: [
                                {
                                    amount: { total: <%=decPrice%>, currency: 'AUD' },
                                }
                            ],
                            redirect_urls: {return_url: "MembershipRenewel.aspx?Confirm=Paid&<%=sString%>"}
                        },
                        experience: {
                            input_fields: {
                                no_shipping: 1,
                            }
                        }
                    });
                },
                onAuthorize: function (data, actions) {
                    return actions.payment.execute().then(function (payment) {
                        return actions.redirect()
                        // The payment is complete!
                        // You can now show a confirmation message to the customer
                    });
                }

sString is set here from VB.NET Code Behind. The values appear as should when debugging.

sString = "Name=" & lblFirstName.Text & "_" & lblSurname.Text & "&Email=" & lblEmail.Text & "&Type=MembershipPayment"

[Anonymous_User]

Have you tried contacting Tech Support - on this page, there's a link at the bottom "Contact Support", on the next page you will need to login and then you can complete and submit a request for assistance.