Why Adalo API Integrations Break
Adalo's External Collections and Custom Actions let you connect to any REST API - payment processors, CRMs, AI services, custom backends. But the integration layer has strict, undocumented requirements that cause silent failures. Your API works perfectly in Postman but returns nothing in Adalo. No error message. No indication of what went wrong.
As certified Adalo Experts, we've built API integrations with Stripe, Twilio, OpenAI, Make.com, and dozens of custom backends. This guide documents every failure point we've encountered.
External Collections vs Custom Actions
| Feature | External Collections | Custom Actions |
|---|---|---|
| Purpose | Display data in lists and screens | Execute operations (send SMS, charge card) |
| Response format | Must be JSON array | Can be any JSON |
| CRUD support | GET, POST, PUT, DELETE | Any HTTP method |
| Use in components | Yes (lists, detail views) | No (action chains only) |
| Authentication | Headers configured once | Headers per action |
The 5 Most Common API Failures
1. Response Is Not a JSON Array
Symptom: External Collection shows 'No Results' despite the API returning data.
Cause: Adalo requires the root response to be a JSON array: [{...}, {...}]. If your API returns {"data": [{...}]} or {"results": [{...}]}, Adalo can't parse it.
Fix: Either modify your API to return a raw array, or use a middleware service (Make.com, Pipedream) to change the response before it reaches Adalo.
2. CORS Errors
Symptom: API works in Postman but fails in the Adalo web previewer.
Cause: The Adalo previewer runs in a browser, which enforces CORS (Cross-Origin Resource Sharing). If your API doesn't include Access-Control-Allow-Origin headers, the browser blocks the request.
Fix: Add CORS headers to your API: Access-Control-Allow-Origin: * (or the specific Adalo domain). If you can't modify the API, use a CORS proxy or call the API through a serverless function.
3. Authentication Header Format
Symptom: API returns 401 Unauthorized in Adalo despite correct credentials.
Cause: Adalo sends auth headers exactly as configured. Common mistakes: using Bearer TOKEN without the space after 'Bearer', using the wrong header name (Authorization vs X-API-Key), or including quotes around the token value.
Fix: Test your exact headers in Postman first. Then copy them character-for-character into Adalo's External Collection auth settings. Watch for trailing spaces and newlines.
4. Custom Action Outputs Disappear
Symptom: Custom Action runs successfully but output values are empty in subsequent actions.
Cause: Every time you save changes to a Custom Action in Adalo, the outputs are reset. You must re-test and re-add the outputs after every edit.
Fix: After editing a Custom Action, click 'Test' to re-run it, then re-map the output fields. This is a known Adalo behavior, not a bug - but it catches everyone.
5. Timeout on Large Responses
Symptom: API calls work for small datasets but fail or hang when returning 500+ records.
Cause: Adalo has an undocumented timeout for External Collection requests. Large payloads exceed this timeout, especially on slow connections.
Fix: Implement server-side pagination in your API. Return 50 records per page with a page parameter. In Adalo, use the 'Load as user scrolls' setting combined with offset parameters.
Building Reliable Integrations
Pattern: Make.com as Middleware
For APIs that don't conform to Adalo's requirements, use Make.com as a transformation layer:
- Adalo calls a Make.com webhook
- Make.com calls the real API
- Make.com transforms the response into Adalo-compatible format
- Make.com returns the clean array to Adalo
This pattern solves CORS, response format, and authentication issues simultaneously.
When APIs Aren't Enough
Adalo's API layer handles simple REST calls, but complex integrations - multi-step workflows, webhooks, real-time data, or OAuth2 flows - push the platform past its limits. When your API integration starts requiring workarounds on top of workarounds, it's time to consider a custom-built solution.
Rehost builds production-grade API integrations - both within Adalo and as custom solutions when you outgrow it. Start your free audit →
FAQ
Why does my Adalo External Collection show no results?
The most common cause is a non-array JSON response. Adalo requires the API to return a raw JSON array at the root level. Check your API response format in Postman - if it's wrapped in an object, you need to modify the API or use middleware.
How do I debug API calls in Adalo?
Adalo doesn't provide request/response logs. Use the External Collection test feature to see the raw response. For Custom Actions, check the browser's developer console (Network tab) while testing in the web previewer.
Can Adalo handle OAuth2 APIs?
Not natively. Adalo supports Bearer token and API key authentication. For OAuth2 flows, use a middleware service like Make.com to handle the token exchange and pass simplified auth to Adalo.