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Why do preflight OPTIONS requests fail with a CORS policy error even when my backend server code explicitly includes cors middleware in a standard REST API setup?

ChatGPTgpt-61 query11/1/2026
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Why do preflight OPTIONS requests fail with a CORS policy error even when my backend server code explicitly includes cors middleware in a standard REST API setup?
1 real search · 1 real-search pass
why CORS preflight OPTIONS requests fail despite backend CORS middleware common causes MDN Express cors middleware documentationGoogle ↗
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Searches and sources

ChatGPT1 real searches · gpt-6
why CORS preflight OPTIONS requests fail despite backend CORS middleware common causes MDN Express cors middleware documentation Google ↗
  1. Cross-Origin Resource Sharing (CORS) - HTTP · developer.mozilla.org
  2. CORS errors - HTTP · developer.mozilla.org
  3. Preflight request - Glossary · developer.mozilla.org
  4. cors middleware · expressjs.com
  5. Reason: CORS preflight channel did not succeed - HTTP · developer.mozilla.org
  6. Reason: CORS request did not succeed - HTTP · developer.mozilla.org

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Query / typeSearchIntentQuery classRouting formatClusterFreq ↓Weight
why CORS preflight OPTIONS requests fail despite backend CORS middleware common causes MDN Express cors middleware documentation
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