In indexer cluster environment, the search head have to be connected to the cluster master and the pass4SymmKey have to be the same as you had deployed to cluster master and indexers as well.
When I experienced this issue in past installations, I redeploy the cluster configuration again just to make sure there is no mistyped on the pass4Symmkey password. Please remember to restart the splunk service when you are removing the configuration to cleanup any issues. I mean, remove the configuration from cluster master, restart splunk service, remove the configuration from Search Head and restart the splunk service. after that, redeploy the configuration again.