3161589 - What went wrong: error checking credentials rejected

I am currently struggling with the setup of an on-premises connector to an S/4 HANA ERP system. 

The VM has already been connected, the connection is working.

The user login does not seem to work, error message results (The stored credentials seem to be invalid).

What went wrong
checking credentials: rejected. Reason:

{"message":"Exception caught, caused by: Max waiting time (20 secs) exceeded for [X-ProxyBridgeRequestId=0f0c955d-42c2-4926-a074-b94bd5b58d56],caused by: Max waiting time (20 secs) exceeded for [X-ProxyBridgeRequestId=0f0c955d-42c2-4926-a074-b94bd5b58d56]","status":500,"error":"Internal server error","timestamp":"xxxxxx"}

)

What could this error message be about? The information we have received from the customer to access their system:

SAP-Router-String: „/H/192.168.94.54/S/3299/H/192.168.94.149/S/3299“
Client: 021
Messageserver: 10.78.1.226
System number: 03
User-Name: SY_ETL_SIGNV

Please check whether you're using the correct SAP router string. With this updated string, it will provide an accurate error message. In this case, the correct router string resulted in the error message "Wrong username or password." This means you can connect to the system, however, the issue is with the username and password credentials used to connect.

KBA , BPI-SIG-PI-DM , Data model / ETL for SAP Signavio Process Intelligence , How To

SAP Signavio Process Intelligence all versions