Schannel failed to receive handshake, SSL/TLS connection failed

1. Why would a TLS handshake fail?
2. What is error 503 SSL handshake error?
3. What does handshake failed mean?

Why would a TLS handshake fail?

An SSL/ TLS handshake error occurs when the client and server can't establish communication over the SSL/TLS protocol (usually due to a protocol mismatch).

What is error 503 SSL handshake error?

This error occurs when Server Name Indication (SNI) is required in the TLS handshake to origin, but the SNI hostname field is either blank or incorrect. To correct this error, enter a hostname value in the SNI hostname field. Often this will match the value specified in the certificate hostname field.

What does handshake failed mean?

SSL Handshake Failed error occurs when the client or server fails to establish a secure connection.