Pennsylvania has signed reciprocal agreements with Indiana, Maryland, New Jersey, Ohio, Virginia, and West Virginia under which one state will not tax employee compensation subject to employer withholding of the other state. These agreements apply to employee compensation only.
What that means is that if you live in PA and work in a reciprocal state, your employer withholds and remits the income tax for your resident state. Because of the reciprocal agreement you pay taxes to your state of residency. It is your responsibility to notify your employer that you are a resident of PA and that your employer should withhold PA tax from your pay and not the income tax of the reciprocal state.
If your out-of-state employer did not withhold PA tax, you file and report your compensation as taxable income to PA and pay the tax.
If your employer withheld the other state's income tax, file for a refund of the tax from the other state. Under the reciprocal agreement, the other state cannot tax the compensation you earned there. The earlier you file for a refund, the more likely you will have your refund by the time your tax is due in your resident state.
You may not claim the PA Resident Credit for any tax you paid, or your employer withheld, and paid to the reciprocal state.