Why should I have to pay when we share kids 50/50?

Again it’s the 50/50 thing. Surely if both parents have their children equal amount of days and nights and they provide for them on the days they have them and everything is spilt down the middle then why should there be any money exchanged? Just because the mother receives child benefit because it’s a hell of a job to appeal against it- they automatically qualify for payments too? There should be no money exchanged if the care is equal. Furious.