How do you make money playing games on inboxdollars?

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I am very close to payout on inboxdollars although it has become a lot harder for me to get there since they have decided to stop sending me paid emails to read. When I questioned them, they said I hadn't completed enough offers. So I pointed out to them all of the offers I HAD completed and never got credit for, and they didn't do anything--they didn't restart my paid emails, nor did they credit the offers. So, I am trying to do things on the site that will get me my $30 since I am less than $2 away. So I started playing the games, but have received no $ for playing them; only "credits" in my game account. How do you make $ in your inboxdollars account by playing the games? Do you have to invest your own money or can you keep playing the free games? Thanks!