3131978 - General troubleshooting for error 400 Bad Request

Possible symptoms:

Connection between SAP DI and ABAP system via SCC stops working, in the SCC ljs_trace.log file, the following error is found (see Note 2452568 for SCC logs and traces):

xxx-xx-xx xx:xx:xx,xxx +xxxx#ERROR#com.sap.core.connectivity.tunnel.client.handshake.ClientProtocolHandshaker#tunnel-client-35-4#          #Invalid status of handshake response: DefaultHttpResponse(decodeResult: success, version: HTTP/1.1)
HTTP/1.1 400 Bad Request
Date: Wed, xx xxx xxxx xx:xx:xx GMT
Content-Type: text/html
Content-Length: 230
Connection: close|
xxxx-xx-xx xx:xx:xx,xxx +xxxx#ERROR#com.sap.core.connectivity.tunnel.client.notification.NotificationClientEventHandler#Thread-38#          #Unable to open tunnel connection: Invalid status of handshake response: 400 Bad Request|
xxxx-xx-xx xx:xx:xx,xxx +xxxx#DEBUG#com.sap.core.connectivity.tunnel.client.AbstractClient#tunnel-client-35-4#          #Tunnel handshake failed! Closing the tunnel channel immediately
com.sap.core.connectivity.tunnel.core.handshake.TunnelHandshakeException: Invalid status of handshake response: 400 Bad Request

In SAP DI tenant, connection test returns:

ERROR
Connection Id: xxx
Status code from service response: 400, Message: Failed to validate connection xxx.

SAP Data Intelligence

KBA , CA-DI , Data Intelligence , BC-MID-SCC , SAP Cloud Connector On-Demand/On-Premise Connectivity , BC-CP-CON-ABAP , ABAP Cloud to On-premise Connectivity service , How To