@iEnam - I have identified and resolved an error I found while testing the recently updated custom Pushover driver along with Rule Machine. It appears that RM already handle the '%' symbol in some special way. Thus, I have changed the two symbols that @garz originally chose with two new ones that will hopefully not be very commonly used in a typical Pushover notification.
Please update your copy of this custom driver and tweak the settings to use the following special characters.