To be able to add the certificate to transaction STRUST in the ABAP system, please make sure that your user has the following authorizations:
For more information, please also check the following Technology Blog Post on SAP BTP Cloud Foundry: switching to higher security level Root Certificate Authority(opens in new tab).
You need to import all certificates to both the SSL Client (Anonymous) as well as the SSL Client (Standard) in the transaction STRUST in your ABAP system.