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A 401 means Mixpanel could not authenticate the request. The credentials were missing, malformed, or not valid for the project you addressed.

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What the Response Looks Like

From /import:

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Which Credentials Each Endpoint Accepts

Don’t rely on a 401 to catch a bad project token on /track. The endpoint can return 200 with a body of 1, which confirms at least one object was well-formed but does not signify a valid project token or secret. Add ?verbose=1 to get a JSON response instead, and check your project’s live view to confirm events are arriving.

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Common Causes

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Service Account Lacks the Required Role

/import requires an Owner or Admin Service Account. A Service Account with a lower role on the project can’t import, even if its username and secret are correct.

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Missing project_id

When authenticating with a Service Account, project_id is required. Without it, Mixpanel cannot tell which project the credentials apply to.

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Wrong Regional Endpoint

Projects with EU or India data residency use different hosts. Send requests to the host that matches your project’s residency. See EU Residency and India Residency.

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Malformed Basic Auth Header

Basic auth expects a base64-encoded username:password pair. A common mistake is encoding only the username, or omitting the colon when the password is empty.

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How to Fix It

Confirm the credential type matches what the endpoint accepts, using the table above. Check the Service Account’s role at Project Settings → Service Accounts. It must be Owner or Admin for /import. Verify your project’s residency and send to the matching host.