Hello,
I just ran into the exact same issue, and might have found an answer for you. After reading through the documentation and getting frustrated, I decided to just copy and past the example GeoJSON file from the Apple docs and replace the coordinates with my own.
Docs: https://developer.apple.com/library/archive/documentation/UserExperience/Conceptual/LocationAwarenessPG/ProvidingDirections/ProvidingDirections.html
Example GeoJSON:
{ "type": "MultiPolygon",
"coordinates": [
[[[-122.7, 37.3], [-121.9, 37.3], [-121.9, 37.9], [-122.7, 37.9], [-122.7, 37.3]]],
[[[-87.9, 41.5], [-87.3, 41.5], [-87.3, 42.1], [-87.9, 42.1], [-87.9, 41.5]]]
]
}
Now I'm not sure if the answer was removing unnecessary tabs/spaces, and copying the example code fixed the issue. Or, as I might be suspecting, that the coordinates for each polygon need to be on the same line. My GeoJSON looked like yours with the latitudes and longitudes broken up one on each line, but all the examples I see from Apple have all their coordinates together like this.
This gave me a headache today, so I hope this answer can help somebody in the future.
Good luck out there!