Unable to establish an SSH tunnel using Redis Desktop Manager

I am trying to connect to an Elasticache Redis Server via an AWS Ubuntu instance and using an ssh tunnel. When I try to configure Redis Desktop Manager to connect via an ssh tunnel and provide credentials and .pem file, I have authentication issues. However, this same .pem file doesn't create issues when I try to connect via shell. Am I missing something here ? should I change the file permission (as for now it is 400). This a screenshot on the errors shown on the RDM system log