Player's contracts only pays him for the 82 games in the regular season. It offers no pay for playoff games. There is a playoff pool provided by the league based on playoff ticket sales, etc. Each team is given a different payout by how far you go in the playoffs.
Each player on OKC this year will receive just over $800k for playing 23 playoff games. That is just under $35,000 per game. SGA made $40 million this year, or just under $488,000 per game.