Amazon Pay Checkout InvalidRequest


I want to use amazon pay system on my site and also using amazon pay sdk which is here

I have successfully created amazon pay button and logged after then gives an error.

Something went wrong

Something went wrong

When contacting Amazon Pay customer service , provide the following info:
Session ID: ce8e4883-fc27-42c9-8b41-5127f7c12b63
Error Code: InvalidRequest

My backend codes;

string privateKey = _appEnvironment.WebRootPath + "\\privatekey.pem";

        // set up config
        var payConfiguration = new ApiConfiguration
            region: Region.Europe,
            environment: Amazon.Pay.API.Types.Environment.Sandbox,
            publicKeyId: "xxxxx",
            privateKey: privateKey
        var client = new WebStoreClient(payConfiguration);
        var request = new CreateCheckoutSessionRequest
                checkoutReviewReturnUrl: "https://localhost:44341/Home/CompleteCheckout",
                storeId: "amzn1.application-oa2-client.bf7916acd8cb4184816c933247dc7ada"

        request.ChargePermissionType = ChargePermissionType.OneTime;

        // generate the button signature
        var signature = client.GenerateButtonSignature(request);

        var model = new HomeModel()
            Signature = signature,
            Payload = request.ToJson()

        return View(model);

My fronted codes;

    <div id="AmazonPayButton"></div>
    <script src=""></script>
    <script type="text/javascript" charset="utf-8">
        amazon.Pay.renderButton('#AmazonPayButton', {
            merchantId: 'yyyyyyyyyy',
            ledgerCurrency: 'EUR',
            publicKeyId: 'xxxxxx',
            sandbox: true,
            checkoutLanguage: 'en_GB',
            productType: 'PayAndShip',
            placement: 'Cart',
            buttonColor: 'Gold',
            createCheckoutSessionConfig: {
                payloadJSON: '@Html.Raw(Model.Payload)',
                signature: '@Html.Raw(Model.Signature)'

I would suggest you to review the parameters using the following hyperlink below:

My included script is
<script src=“ ”>