To pay for something "out of your own pocket" means to pay for it with your own money. This is a common expression that's easy to remember if you imagine carrying all your money around in your pockets, and then pulling the money out of your pocket to pay for something.
You can only talk about someone paying out of their own pocket:
She paid for the trip out of her own pocket.
It doesn't make sense to talk about one person paying out of another person's pocket.