Order properties not persisting ?

Im developing a payment plugin for Ideal, on "postProcessPayment" im setting AuthorizationTransactionID and PaidDateUtc.

public void PostProcessPayment(PostProcessPaymentRequest postProcessPaymentRequest)
        {
            Transaction transaction = getTransaction(postProcessPaymentRequest);
            postProcessPaymentRequest.Order.AuthorizationTransactionId = transaction.Id;
            postProcessPaymentRequest.Order.PaidDateUtc = DateTime.Now;
            _httpContext.Response.Redirect(transaction.IssuerAuthenticationUrl.ToString());

When returning from the thirdparty payment portal i call a function to verify the payment and check the AuthorizationTransactionID.

string trxid = Request.QueryString["trxid"];

                if (order.AuthorizationTransactionId == trxid)

Yet both the AuthorizationTransactionId and PaidDateUtc are null.
Am i missing something ? (Save?)

They are not persisted because you do not save them before redirecting to third-party site:
1. Load appropriate order instance and set required values
2. Update order (using IOrderService)
3. and now redirect...