I accidentally made a mistake during my federal tax return for 2021 during the W2 income/tax data entry portion. As a result, the system interpreted that I owed $4,000 to the IRS. Before realizing the mistake I went ahead and made the payment (which the IRS has not withdrawn yet).
Now I am filing a 1040X to correct this error and am instead supposed to receive a refund of $5,000. On the 1040X Form Line 18: "Overpayment, if any, as shown on original return or as previously adjusted by the IRS" would I need to enter the $4,000 for the payment I made in error (even though it has not been withdrawn by the IRS yet)? I just want to make sure that I get my correct refund back of $5,000 and am not charged the $4,000 over the mistake on the original filing.
Separately, would I need to file the 1040X first with the IRS before I can amend my state tax filing since the original error transferred to the state filing portion as well?
No, you didn't show any overpayment on the original return so you wouldn't say that there was one. The IRS will cash your check and then refund it as part of the $5,000 they will owe you when you file the amended return.
You can file both federal and state amended returns at the same time.
Since the IRS has not cashed your check, they may adjust your return automatically, especially if your error is obvious and they can determine it based on the W-2 entry you made, so it may be wise to wait until they cash your check before you submit the amended return.