I already paid in full to file my taxes. Why does one of the states I filed for still require more money and won't tell me what I owe?

Why do you say you paid them in full?  What do you mean it says you still require more money but won't tell you what you owe?  Which state?  Please provide more details on your situation.

You would not know that you paid them until you filed your return.  Your return is a reconciliation of what you owe versus what you paid, so if you paid less than what your return says you owe. In general, your home state will tax all in come from all sources.  What you will do is you will file a nonresident return for the states that you do not reside in, but you visit for work and earn money in.  When you file, you will fille out your nonresident states first.  Then you will fill out your resident state, claiming a credit for taxes paid to the nonresident states on your home state return.  You may or may not still end up owing money to your resident state depending on whether or not their tax rate is higher or lower than your nonresident state.  If the non resident state had a higher tax rate than your resident state, your credit will be limited to the amount of tax you would have paid to your resident state.  They will not give you a refund of the taxes you paid to the nonresident state. 

You should be able to see what you owe by looking at the top of your screen where the states are listed.  If you do not see the state you are talking about then you will just need to click on the little arrow next to the state to see more states. 

Multiple States

File Non Resident State Return