[keycloak-user] Admin CLI - how to a a builtin protocol Mapper to a Client

Hi I am trying to add the built-in protocol mapper "realm roles" to a client using the Admin CLI. I must have tried 500 syntactic combinations for the "--set" parameter; they all result in either no error (but no mapper added to the client), or a Java exception (com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of VALUE_STRING token). Does anyone have an example that can be shared of successfully using the Admin CLI for this operation, please? Keycloak version is 6.0.1 Regards Bruce