When using the Mixpanel API to update a user profile with a new list attribute like "subscriptions" via the union operation, Mixpanel should add the specified values to the list property, ensuring no duplicates, and create the profile if it does not exist. This is confirmed in the API documentation: "Adds the specified values to a list property on a user profile and ensures that those values only appear once. The profile is created if it does not exist" Union To List Property, Ingestion API - user-profile-union.
However, you mention that sometimes users are not updated, even though you see the data reaching the API in debug mode. Here are some possible reasons, based on the knowledge sources:
1. Profile Creation on First Union:
The union operation should create the profile if it does not exist. However, if the profile is not being created, ensure that your API request includes all required fields: $token, $distinct_id, and the $union object with the correct structure. If any of these are missing or malformed, the update may silently fail for that user. The API expects a JSON object like:
{
"$token": "YOUR_PROJECT_TOKEN",
"$distinct_id": "USER_ID",
"$union": {
"subscriptions": ["sub1", "sub2"]
}
}
Ingestion API - user-profile-union
2. Verbose Debugging:
Use the verbose=1 query parameter in your API call. This will return a JSON object indicating the success or failure of each update, including error messages if the request was not successful. This can help you pinpoint if the API is rejecting some updates and why Ingestion API - user-profile-union.
3. New Attribute Handling:
If "subscriptions" is a new property, it should be created on the user profile the first time you send a union update. If the property does not exist, union should initialize it with the provided values. If you see no update, double-check that the property name and value types match what Mixpanel expects (property name as a string, value as an array of strings or numbers).
4. API Response and Error Handling:
If you see the data flowing to the API but not reflected in the user profile, check the API response for each request. A status of 1 means success, 0 means failure. If you get a 0, the response should include an error message explaining why the update failed.
5. Strict Mode and Other Parameters:
