The version number (CFBundleShortVersionString) is a user-visible string for the version of the bundle. The required format is three period-separated integers, such as 10.14.1. The string can only contain numeric characters (0-9) and periods.
Each integer provides information about the release in the format [Major].[Minor].[Patch]:
Major: A major revision number.
Minor: A minor revision number.
Patch: A maintenance release number.
This key is used throughout the system to identify the version of the bundle. The version number is shown in the App Store and that version should match the version number you enter later in App Store Connect.