AMQ9641E: Remote CipherSpec error for channel … to host …

EXPLANATION:
The remote end of channel … on host … has indicated a CipherSpec error ‘SSLCIPH(‘ ‘) -> SSLCIPH(????)’. The channel did not start.

EXPLANATION:
The remote end of channel … on host ‘….’ has indicated a CipherSpec error ‘SSLCIPH(TLS_CHACHA20_POLY1305_SHA256 ) -> SSLCIPH(…)’.

Colin’s comments.

1. I had ServerConnectionParms defined in my mqclient.ini stansa CHANNELS: or environment variable MQSERVER defined. These cannot be used for a TLS channel
2. The server’s cipher spec must be at a higher level than the client. For example with a client cipher spec of ANY_TLS12_OR_HIGHER, during the handshake it agreed with the queue manager on TLS_CHACHA20_POLY1305_SHA256,  a TLS 1.3 cipher spec.   This was then checked by the channel code which was ANY_TLS12, and was not supported.   Hence the AMQ9641E message. 
3. If the qm.ini, SSL stanza has been changed from AllowTLSV13=NO to AllowTLSV13=YES, this will cause the problem in 2. above.