Could not add system &1

What causes this issue?

A system could not be added to a cluster in the configuration UI. There
could be various reasons for this. Check your configuration as described
below.

System Response

A system could not be added to a cluster in the configuration UI.

How to fix this error?

<ZK>1. Check the system state in TMS</>
Call transaction STMS in your system and navigate to 'System Overview'.
Select the system in question and run the following tests: 'Connection
Test', 'Transport Directory Test', and 'Transport Tool Check' (see the
'SAP System' menu).
If errors occur, contact your system administrator.

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

<ZK>2. Validate the system in the configuration UI of the Central Change
and Transport System</>
Call transaction SZENTMS, select the system in question, and validate it
by choosing 'Validate'.
If errors occur, follow the instructions on the screen.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.