You have Prepared the Central Instance for using SSO with client certificates.
To enable the use of SSO with Client Certificate, you have to activate the use of SSO on the SAP Logon.
Select an entry in the SAP Logon window and choose → Properties Advanced.
Select Enable Secure Network Communications.
In SNC name, enter:
p:< DN name of the AS ABAP >
For a DN name of the AS ABAP, enter the distinguished name of the AS ABAP as configured on the central instance parameter snc/identity/as
Choose OK to confirm your entries.
The SAP Logon window now displays an icon with a key beside the system entry. This indicates that Single Sign-On is active for the system. Users can log on to the AS ABAP from the SAP Logon.