This error is typically a result of one of the following: A test order was placed for an upsell but was not initiated by placing the initial order. The order form is not set to pass the contact details to the up sell url. The javascript code wasn't placed before the closing body tag in the page's code The WordPress plugin was not installed or it was installed but the page was created in OptimizedPress. If it was, the javascript code needs to be entered into the body of the page via OptimizedPress's SEO code area.