This error means the connected app returned a response that Zapier could not process — typically HTML instead of JSON, an unexpected data structure, or a malformed payload. Check the Zap History for the raw response, verify the app's authentication, and ensure the API endpoint returns valid JSON.
What does "Zap error: app returned invalid response" mean?
When Zapier shows "Zap error: app returned invalid response," the action step sent a request to the connected app and received a response that Zapier could not understand. Zapier expects every app to return structured data (JSON), and when the response is HTML, XML, empty, or otherwise malformed, this error appears.
The most common cause is the classic JSON/HTML mismatch: the API returns an HTML error page instead of JSON data. This happens when authentication fails (the API redirects to a login page), the API endpoint changed, the server is in maintenance mode, or the request triggers a rate limit that returns HTML. Zapier tries to parse the response as JSON and fails.
This error can also appear when the app changes its API version or response format. An app that returned {"id": 123, "name": "John"} might start returning {"data": {"id": 123}, "meta": {}} after an API update. The new wrapper structure confuses Zapier's field mapping, causing it to report an invalid response even though the data is technically valid JSON.
Common causes
The app returned HTML instead of JSON
usually a login page, error page, or maintenance notice
Authentication tokens expired and the
app returned an auth error response instead of data
The app's API endpoint URL
changed and the old URL returns a 404 page
The app updated its API
response format, breaking Zapier's expected data structure
The response body is empty or
null, which Zapier cannot parse as valid data
A rate limit or quota
exceeded response was returned in an unexpected format
How to fix invalid response errors in Zapier
Open Zap History and click the errored run. Expand the failed action step to see the full response data. If you see HTML tags (<!DOCTYPE, <html>), the API is returning a web page instead of JSON. Check the app connection in My Apps — reconnect the account to refresh authentication tokens. If the app's API URL changed, update the Zap step with the new endpoint.
If the response is valid JSON but in a different structure than expected, you may need to reconfigure the Zap step. Some apps allow choosing API versions — set it to the version your Zap was built for. Use Zapier's 'Troubleshoot' tab in the errored run for AI-powered diagnosis. For webhook-based actions, verify the receiving app's webhook endpoint is active and returning application/json content type. For complex app integrations with frequent response format issues, RapidDev can help build stable API middleware.
Prevention tips
- Check the Zap History raw response first — it shows exactly what the app returned so you can identify HTML, empty, or malformed responses
- Reconnect the app in My Apps when you see invalid response errors — expired tokens are the most common cause
- Use Zapier's Troubleshoot tab for AI-powered diagnosis of the specific response issue
- Pin the API version in the Zap step configuration (if available) to prevent future API changes from breaking your Zap
Still stuck?
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My Zapier Zap shows 'app returned invalid response' and the response body contains HTML instead of JSON. The app is a CRM. How do I fix the authentication and get valid JSON responses?
Diagnose why this Zapier action step is receiving an invalid response from the connected app and help me fix the connection.
Frequently asked questions
What does "Zap error: app returned invalid response" typically mean?
The connected app returned data that Zapier cannot parse — most commonly HTML instead of JSON. This usually indicates an authentication failure (login redirect), a changed API endpoint, or a server error returning an HTML page.
How do I see the raw response that caused the error?
Go to Zap History, click the errored run, and expand the failed step. The response section shows the raw data returned by the app. Look for HTML tags, error messages, or unexpected data structures.
Will reconnecting the app in Zapier fix the invalid response error?
If the cause is expired authentication, yes. Go to My Apps in Zapier, find the affected app, and reconnect it. This refreshes the OAuth tokens and should restore valid JSON responses.
Can API version changes cause invalid response errors in Zapier?
Yes. When an app updates its API and changes the response structure, Zapier may fail to parse the new format. If the Zap step allows choosing an API version, pin it to the version your Zap was built for.
Does the invalid response error consume Zapier tasks?
The errored Zap run counts as a task but the action did not succeed. Check Zap History to see how many tasks were consumed and consider replaying successful runs that were followed by the error.
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