Unable to connect private PostgreSQL instance from looker

I am not able to connect private PostgreSQL instance from looker

My database instance hosted on GoogleCloud SQL. It has only private IP and using shared VPC.  Not able to connect from looker . 

Its giving following error 

Cannot connect: connection refused: Java::OrgPostgresqlUtil::PSQLException: The connection attempt failed. JDBC string: jdbc:postgresql://10.125.242.35:5432/cpp?tcpKeepAlive=true&ssl=true&sslfactory=org.postgresql.ssl.NonValidatingFactory&sslmode=prefer

Please help me to resolve the issue.