While MacroDroid can't detect toast messages alone another app can that can be integrated with MacroDroid.
Install and setup the Toast Source app. Make sure the show as notifications option is enabled.
This app can help you find out which program is abusing "toasts" notifications.
play.google.com
In MacroDroid, use the notification received trigger to detect any popup messages.
With the clear notifications action, remove the notification.
You can then compare the notification text and your message in an if clause to see if they match.