What does HRESULT 0x803D001A (WS_E_PROXY_REQUIRES_NTLM_AUTH) mean?

WS_E_PROXY_REQUIRES_NTLM_AUTH

WS_E_PROXY_REQUIRES_NTLM_AUTH is a Windows Web Services API HRESULT. It means that the proxy rejected the offered authentication scheme and requires NTLM authentication.

Diagnostic discriminator: Confirm that the intended proxy issued the NTLM challenge and that organizational policy permits NTLM for this connection. If the request reaches the proxy but authentication negotiation stops at NTLM, routing and origin availability are separate questions. Preserve proxy identity, connection reuse behavior and client account context without exposing challenge-response material.

What to check for WS_E_PROXY_REQUIRES_NTLM_AUTH

• Verify the proxy authentication policy, user context and NTLM availability for the client process.
• Check proxy host identity and connection behavior before enabling integrated credentials.
• Do not forward NTLM credentials through an unexpected proxy or an untrusted network path.

Microsoft documentation