I’m trying to send backend events to an EU Residency Mixpanel project.

I’m trying to send backend events to an EU Residency Mixpanel project. I’m using: POST https://api-eu.mixpanel.com/track?verbose=1&ip=0 with headers:

and raw JSON body:

{
  "event": "Test Event",
  "properties": {
    "token": "MY_PROJECT_TOKEN",
    "distinct_id": "test-user-1"
  }
}

But I always get:

{
  "error": "data, missing or empty",
  "status": 0
}

I get the same error even with hardcoded values and even with an intentionally wrong token. Frontend JS tracking works fine, so this seems isolated to backend ingestion. Can you confirm the correct EU backend tracking endpoint and whether /track expects raw JSON or a data= field?