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I don't understand why I have to pay for an extra $50 fee? or

I don't understand why I have to pay an extra $50 fee?

Are both correct?
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PreciousJonesI don't understand why I have to pay an extra $50 fee.
This one is correct.
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To pay for something is to exchange money in return for it.

If I pay for a shirt, I give someone money and they give me the shirt.

It's impossible to pay for a fee. You will not receive a fee in return for your money. "fee" is a reference to the money that is exchanged - not a reference to something you receive because you have paid.

CJ