We are using the Unreal Marketplace Plugin for UE4 4.21 and we get a warning when compiling the project:
LogPluginManager: Warning: Engine version string in ../../../Engine/Plugins/PlayFab/PlayFab.uplugin could not be parsed ("4.21")
It looks like the engine requires this to be formatted as: major.minor.patch
Right now it's just a warning, but we like to compile with warnings-as-errors