rds connection from telnet or pgAdmin - what host?

I created DB instance and obtained such endpoint:
tripbook-db.cvvxhyaiehrw.us-east-2.rds.amazonaws.com
with port 5430

I tried to log in via pgAdmin or telnet but no success.

telnet supposed to work like this : telnet <endpoint> <port> but its' not working:
telnet tripbook-db.cvvxhyaiehrw.us-east-2.rds.amazonaws.com 5430

DB is available and public open.