ERROR_HTTP_HEADER_ALREADY_EXISTS

Code: 12155 (12155)

As HRESULT:

S: 0 (Success)
C: 0 (Microsoft-defined)
N: 0 (Not an NTSTATUS value)
Facility: 0x000 (FACILITY_NULL: Default)
Code: 0x2f7b (12155)

As NTSTATUS:

Sev: 0 (STATUS_SEVERITY_SUCCESS)
C: 0 (Microsoft-defined)
Facility: 0x000 (Default)
Code: 0x2f7b (12155)

Documented in Win32

Error Messages (wininet.h): 12155

The header could not be added because it already exists.