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WININET_E_HEADER_ALREADY_EXISTS
WININET_E_HEADER_ALREADY_EXISTS is a WinINet HRESULT. It means that the application tried to add a header that WinINet considers already present in the request or header collection. A duplicate can be harmless only when the protocol explicitly allows repeated values; otherwise it can alter request semantics.
What to check
- Inspect headers already set by WinINet and the application before adding another value.
- Replace, coalesce or intentionally append the header using the documented modifier instead of adding it blindly.
- Pay particular attention to headers such as
Content-Length,Host,AuthorizationandCookie.
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