Percona Audit plugin preventing the MySQL server from starting

I first installed the Percona audit plug-in on our MySQL server (the version of my MySQL server is 5.5.38), then I stopped the mysql server, and then in the my.cnf file, added the variables like "audit_log_policy, audit_log_rotation_size, audit_log_file_location, etc.," with my requirements. But when I try to start MySQL, the error "unknown variable" audit_log_policy = ALL " is displayed, which prevents the MySQL server from starting. Can any one help me solve this problem?