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If an API works in Postman but fails in the browser, it’s usually due to environment differences (headers, CORS, auth, cookies, etc.)
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✅ If API works in Postman but fails in Browser:
1️⃣ CORS issue (Most common)
Browser blocks cross-origin requests, Postman doesn’t. Backend must allow frontend origin.
2️⃣ Preflight (OPTIONS) not handled
Browser sends an OPTIONS request first. If server doesn’t allow it → request fails.
3️⃣ Missing Headers
Authorization, Content-Type, or custom headers may not be sent from frontend properly.
4️⃣ Authentication issue
Token or cookies may not be attached in browser request.
5️⃣ HTTPS vs HTTP (Mixed Content)
Browser blocks HTTP APIs when frontend is running on HTTPS.
6️⃣ CSRF Protection
Backend may require CSRF token for browser requests.
7️⃣ Cookie / SameSite policy
Browser enforces cookie security rules, Postman doesn’t.
8️⃣ Wrong API URL / Environment
Frontend may be pointing to different environment.
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🔍 How I debug:
Open Browser DevTools → Network tab → compare request with Postman → identify difference → fix backend or frontend config.
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2 months agodnoch
Multiple potential issues. First start with what kind of failure you’re getting in the browser. If it’s a CORS issue, it will tell you as much in the network tab. Otherwise take a look at the http response code for your next clue - 401 response likely means you’re not setting your Auth headers correctly; 400/500 error means you’re probably not formatting your payload correctly. Lastly, make sure you’re using the correct request method (GET/POST/PATCH/etc)
2 months agocode_soubhik
I would first check the CORS and status code from browser, if it's cors we add our origin in the services if not I will check the status code and try to debug the code.
3 months agoaspicyengineer
90% of the time it’s a CORS issue if it works in postman but not in the browser. Update the API header to support localhost or disable CORS in the browser for development.
3 months agozagham_abbas786
There are two possible issues. One is cors and the other could expired ssl certificate
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