Up sell down sell plug in for your client to increase traction or save the data
Modern browsers now consider displaying a custom message to be a security hazard and it has therefore been removed from all of them. Browsers now only display generic messages

Note:  Custom message will only be displayed if the user selects 'cancel' on the generic exit message.

Demo app's editor link

https://bubble.io/page?name=index&id=exit-handler&tab=tabs-1