Problem
The message received was unexpected or badly formatted (in .NET Core 3.1)
HRESULT error: SEC_E_ILLEGAL_MESSAGE (0x80090326)
Cause
This error happens during the TLS protocol negotiation with the server.(Mtls)
I have already checked the cipher suites for both Server and Client no missing ciphers.
The .NET Core 3.1 API request worked previously on this server hosted on AWS.
Dev Machine runs on Windows Home 11.
I was able to make API calls through Postman to the same server without any exceptions.
I've tried all solutions suggested on stack overflow
Server Ciphers
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xc02f) ECDH secp256r1 (eq. 3072 bits RSA) FS
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (0xc030) ECDH secp256r1 (eq. 3072 bits RSA) FS
Client Ciphers
[C02F] TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
[C030] TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
[009E] TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
[009F] TLS_DHE_RSA_WITH_AES_256_GCM_SHA384
[C02C] TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
[C02B] TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
[C024] TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
[C023] TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
[C028] TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
[C027] TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
[C00A] TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
[C009] TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
[C014] TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
[C013] TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
[009D] TLS_RSA_WITH_AES_256_GCM_SHA384
[009C] TLS_RSA_WITH_AES_128_GCM_SHA256
[003D] TLS_RSA_WITH_AES_256_CBC_SHA256
[003C] TLS_RSA_WITH_AES_128_CBC_SHA256
[0035] TLS_RSA_WITH_AES_256_CBC_SHA
[002F] TLS_RSA_WITH_AES_128_CBC_SHA
