Power Automate发送POST请求触发Internal Server Error但Postman可正常调用的问题排查求助

Let's break down the most likely causes for this discrepancy and how to fix them—since your API clearly works with Postman, the issue is almost certainly a subtle difference in how Power Automate sends the request:

1. Mismatched Request Headers #

Postman handles headers automatically and reliably, but Power Automate often needs explicit configuration:

• Content-Type: Double-check that Power Automate sends Content-Type: application/json (if your request body is JSON). Postman adds this by default when using raw JSON, but Power Automate might leave it blank or set it to an incorrect value like text/plain.
• Extra Auto-Added Headers: Power Automate sometimes injects headers like Expect: 100-continue which some APIs don’t handle gracefully. Try manually overriding this header with an empty value or removing it entirely in the HTTP connector’s advanced settings.
• Side-by-Side Header Comparison: Use Postman’s "Code" feature (top-right corner) to generate a cURL command of your working request, then cross-reference every header with what’s set in Power Automate. Even a tiny difference (like an extra space in a header value) can trigger a 500 error.

2. Request Body Format or Encoding Issues #

Even minor syntax errors or encoding mismatches can break the API’s parsing logic:

• Validate JSON Syntax: If your request body is JSON, use an online validator to check for typos (missing commas, mismatched quotes) in Power Automate’s body field. Postman auto-formats JSON, but manual input or dynamic content in Power Automate can easily introduce errors.
• Special Character Encoding: If your input text includes non-ASCII characters (accents, emojis, etc.), ensure Power Automate uses UTF-8 encoding. Postman handles this automatically, but dynamic content in Power Automate might default to a different encoding if not configured properly.
• Exact Body Copy Test: Copy the raw request body directly from Postman into Power Automate’s body field (use plain text mode, not dynamic content) and run the flow. If it succeeds, the issue is with how your flow generates the body dynamically.

3. Basic Authentication Handling Differences #

Postman encodes username:password to Base64 correctly, but Power Automate can mess this up in a few ways:

• Use the Built-in Basic Auth: Instead of manually adding an Authorization header, select "Basic" as the authentication type in the HTTP connector, then input your username and password directly. This ensures Power Automate handles encoding correctly, even if your password has special characters like @, &, or spaces.
• Verify Manual Header Encoding: If you must use a manual Authorization header, generate the Base64 string using Power Automate’s base64(concat('your-username', ':', 'your-password')) function to avoid encoding mistakes.

4. Timeout & Retry Configuration #

Your API’s execution time is ~3.36 seconds, which might be hitting Power Automate’s default limits:

• Adjust Request Timeout: In the HTTP connector’s advanced settings, increase the timeout to at least 10 seconds. A premature timeout can interrupt the API mid-processing, leading to a 500 error.
• Disable Retries Temporarily: Your flow retries 4 times, which might trigger server-side rate limiting or protection mechanisms. Turn off retries (set "Retry policy" to "None") and test a single request. If it succeeds, the issue is with repeated rapid requests.

5. Power Automate Environment/Network Restrictions #

Power Automate runs in Microsoft’s cloud environment, which might have proxy or firewall rules that modify your request:

• Check Tenant Network Policies: If your organization restricts Power Automate’s outbound traffic, the request might be altered before reaching the API. Compare the source IP of your Postman request vs. Power Automate’s (you can get this from the API server logs).
• Test in a Personal Environment: Try running the flow in a personal Power Automate environment (if you’re using a work/school tenant) to rule out organizational restrictions.

6. Check API Server Logs #

This is the fastest way to get to the root cause. Ask your API provider (or check your own server logs) for details on the error when Power Automate sends the request. The logs will likely tell you exactly what’s wrong—whether it’s a malformed body, invalid auth, or a header that the API rejects.

Quick Diagnostic Test #

1. In Postman, go to Code > cURL to get the exact command for your working request.
2. Replicate every part of this cURL command (headers, body, auth) exactly in Power Automate’s HTTP connector.
3. Run the flow—if it works, the problem was with your original flow configuration. If not, use a tool like Fiddler to capture both requests and compare them side-by-side to spot the difference.

内容的提问来源于stack exchange，提问作者Stefan