Some teams have opted to add a financial incentive to the Singles matches, where the Loser pays the Winner a token £1, based on the result of the game (ie not per leg).
Quids In is only enacted if both teams have opted in. You can see who has opted in on the team’s page on this website, eg /team/profile/frenches-exiles/
It’s a slightly divisive subject, where some teams view it as some added fun, while others view it as pointless. In the past, both leagues have had a history of trying other things, eg half a pint for the winner, and it’s an area where thoughts appear to gradually change over time (in both directions).