@chris Thankyou for the response, I tried below fix, but still getting the same error.
I moved it to /var/www/medapp/rds-combined-ca-bundle.pem
-rwxr-xr-x 1 medappuser medappuser 43888 May 5 11:07 rds-combined-ca-bundle.pem
SetEnv MONGO_URL mongodb://:@XXXXXXXXX.docdb.amazonaws.com:27017/?ssl=true&ssl_ca_certs=/var/www/medapp/rds-combined-ca-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false