FirebaseAnalytics event name rules

When using FirebaseAnalytics to track event in mobile app, it must be following some rules.

• Event name is case sensitive, so trackTapButton and TrackTapButton is counted as separate event
• Don’t use reserved prefixes and event name
• Must start with letter
• Use only letter, number and underscores. So track-tap-button is invalid event name

Source: https://support.google.com/analytics/answer/13316687