Difficulties connecting pgAdmin 4.4.15 to Postgres RDS

1. I am constrained to use pgAdmin 4.4.15. Upgrade is not an option
2. Conventional, command-line connection goes from my workstation, to PuTTY
terminal on a "dmz", and from the dmz to an intermediate, client server.
These values do establish a connection.
Every attempt to connect via pgAdmin results in an error unable to connect
to server: Failed to create the SSH Tunnel. Error: Could not establish
session to SSH gateway
3. I use all the values from the command line connection in the pgAdmin
connection ... but the failure persists.

Is there some unanticipated setting in RDS that prevents this pgAdmin
connection?

Regards,
--
Gus

gus(dot)spier(at)gmail(dot)com
540-454-3074

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