Hi Jurgen,
Thanks for the tip. You answered exactly what I wanted to know. I wanted to connect to a paper trading account so I can start placing orders to it and test my algorithmic trading system working.
I logged into my IB live account on their web app, went to Settings > Paper Trading Account and got this screen.

1. I reset my password there for my paper trading account.
2. I went to ?to try to log into the paper trading account for my Gateway server.
However the Gateway tells me "Invalid username password combination".
So how do I create a session to the paper trading account (not the live account) for my Gateway server to start placing orders? I've tested all the REST API endpoints with the live accounts such as fetching contract details and historical marketdata. Everything is working... and now I just want to test placing orders.