To pay for s.t. [N-]; to transact a deal by paying and receiving [mag-]; to charge s.o. for s.t. [ma-].
The -an imp. focuses on the object that is being paid for. The paN--un imp. focuses on the money used to pay for s.t. The pa--an imp. focuses on the object that one is charging s.o. to pay for.
When it comes to buying s.t. big, you should transact the deal in front of the elders in the village.
If you have a big debt, whenever you have money use it to pay your debt right away.
To charge or have s.o. pay for s.t.(focus).
Have him pay for that fish because you can't finish it.