I recently found that a deactivated pop-up is included in the "start from scratch" funnel template. When a checkout element is added to the page the popup MUST be DELETED for the checkout form to work - even if the pop-up is not activated. It took me several days to find the problem with support. Please detect the problem and display an appropriate warning "Pop-up Detected - Please Delete Pop-Up on Checkout Page". The current error just says "wait a few seconds & try again"