When calling the Create Stream Marker API (Reference | Twitch Developers), the documentation says that the created_at value should be “The UTC date and time (in RFC3339 format) of when the user created the marker.”.
However the time returned includes nanoseconds, which isn’t valid RFC3339.
Here is a sample response from creating a stream marker
{"id": "6cc96f22d0c6f405414fe63d241aa156", "created_at": "2025-03-01T10:10:45.865184169Z", "position_seconds": 89, "description": "test"}