Configuration error; connection missing in customizing

What causes this issue?

In the current client of SAP NetWeaver Application Server (SAP NetWeaver
AS) ABAP, the database connection required for linking users of SAP
NetWeaver AS ABAP with the DBMS is missing.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Enter a database connection with the supported type and the current
client in maintenance view USR_DBMS_SYSTEM.
Ensure that the database connection is maintained in transaction DBCO
and the user for the database connection has appropriate authorizations
in the DBMS.
For more information, see SAP Note 1836006.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.