How do you claim a bounty I've put the guy in hospital but no money 

You have to hospitalise the player.

To expand on what Kwyy said. To collect a bounty, when you go to attack the person who has a bounty on their head you select the face icon when attacking that says "Attack and hospitalize" instead of the gun icon or the money icon. Then when you finish the attack successfully and check your events you should see that the attack log also includes that you collected the bounty.