Guy,
There are many ways to create a KML file. I think the key is, to get to know the way you prefer and be aware of what can go wrong.
Our recommended method is to use the "Create KML Course" function in the MapRun Console:
https://console.maprun.net/#/event_create_filesOn that page, tap the "How to Use" button for instructions. It is possible to import and edit a course created in PurplePen (.PPEN file) or a course created in any other system that can create IOF XML files.
Peter