ShopMessage uses a combination of click-through and view-through attribution, with a 72-hour attribution window. The majority of sales are tracked via click-through attribution. This is because Facebook does not provide any information about views unless the user responds to the message.
If a user has ever responded to your Facebook Page, using a quick reply, a session ID will be identified, allowing us to track a view-through conversion. We can only track the view-through conversions if a user is within the same browser. There are certain instances where we will not be able to track the user within the same browser.
If a user simply views a message from your Facebook page and then makes a purchase, without ever using a quick reply, we would not be able to track that purchase.
In addition to our dashboard attribution, ShopMessage also adds UTM parameters to all links from Messenger, so you should be able to track visits and purchase using Google Analytics, or any analytics tool of your choice.