Troubleshooting API by Zapier

Symptom

When you try to create a new API by Zapier connection from the Apps page, the setup flow does not finish. The connection is not created.

Causes

• Required fields were not completed for the chosen authentication type.
• OAuth2 credentials (client ID, client secret, authorize URL, or token URL) are incorrect.
• The OAuth2 app does not accept Zapier's redirect URI.

How to fix it

1. Create a new API by Zapier connection from the Apps page.
2. Double-check all required fields for your authentication type. Refer to How to get started with API by Zapier for the required fields for each auth type.
3. If you're using OAuth2, confirm your app's redirect URI is set to: https://zapier.com/dashboard/auth/oauth/return/App235435CLIAPI/
4. If you provide a Test URL, make sure it returns a 2xx response when your credentials are valid.

Symptom

A 401 (Unauthorized) or 403 (Forbidden) error appears in Zap history when an API by Zapier step tries to send a request.

Causes

• Your API key or OAuth2 token has expired or been revoked.
• Your OAuth2 scopes do not include the permissions the endpoint requires.
• The API key does not have access to the specific resource you're requesting.

How to fix it

1. Go to the Apps page and find your API by Zapier connection.
2. Check that the connection is still active. If the connection shows an error, create a new connection with updated credentials.
3. Verify with the API provider that your credentials have the required permissions for the endpoint you're calling.
4. If you're using OAuth2, confirm that the scopes in your connection match what the endpoint requires. You may need to create a new connection with updated scopes.

Symptom

A "Domain not allowed" error appears when your Zap step tries to send a request using API by Zapier.

Causes

• The domain in the step URL does not match the domain filter you set when creating the connection.
• A typo in the step URL or the domain filter.
• A missing wildcard prefix (e.g., you filtered for example.com but the endpoint uses api.example.com).

How to fix it

1. Open the Zap step with the error and check the URL.
2. Compare it to the domain filter in your API by Zapier connection. The step URL's domain must match one of the allowed domains.
3. If you need to access a subdomain like api.example.com, make sure the domain filter uses a wildcard (e.g., *.example.com) or includes the specific subdomain.
4. If the domain filter needs to change, create a new connection with the correct domains.

Symptom

An HTTP error status code (such as 400, 404, 429, 500, 502, or 503) appears in Zap history when an API by Zapier step runs. These errors come from the API you're calling, not from Zapier.

Causes

• 400 Bad Request: The request body or parameters are formatted incorrectly.
• 404 Not Found: The endpoint URL is wrong or the resource does not exist.
• 429 Too Many Requests: You've exceeded the API provider's rate limit.
• 500/502/503: The API provider's server is experiencing issues.

How to fix it

1. Check the endpoint URL for typos.
2. Review the request body and parameters against the API provider's documentation.
3. If you're exceeding rate limits, reduce the frequency of your Zap or add a Delay step before the API by Zapier step.
4. For 5xx errors, wait and try again. If the errors persist, check the API provider's status page.

Symptom

Your Zap step fails with a JSON parsing error when API by Zapier tries to send the request body.

Causes

• Missing or extra quotes, brackets, or commas.
• Mapped fields that contain special characters (like quotes) that break the JSON structure.
• Trailing commas after the last item in an object or array.

How to fix it

1. Copy your request body and paste it into a JSON validator like jsonlint.com.
2. Check that all mapped fields are properly quoted. For example, {"name": "{{name}}"} — if {{name}} resolves to a value containing a quote, the JSON will break.
3. If a mapped field might contain special characters, consider using a Formatter step to escape the value before mapping it into your JSON body.

Symptom

Your Zap uses the New Item from API trigger, but no new runs appear in Zap history even though the API has new data.

Causes

• The Response Filter path does not match where the array is in the API response.
• The Dedupe Key does not return a unique value for each item.
• The API endpoint is not returning new data.

How to fix it

1. Test the API endpoint directly (using a tool like Postman or your browser for GET requests) to confirm it returns the data you expect.
2. Check the Response Filter path. It must match the exact location of the array in the response. For example, if the response is {"data": {"results": [...]}}, the filter path should point to data.results.
3. Verify the Dedupe Key returns a value that's unique for each item (like an id field). If two items share the same dedupe key, the trigger treats them as duplicates and skips one.