If I enter the wrong PY IP PIN when submitting my return, will it be rejected, or will it still be accepted but cause issues with the return further down the road?

An IP PIN helps the IRS verify a taxpayer’s identity and accept their electronic or paper tax return. If you enter an incorrect IP PIN, it will be rejected until you submit it with the correct IP PIN or you file on paper. If the same conditions occur on a paper filed return, the IRS will delay its processing and any refund you may be due for your protection while the IRS determines if it’s yours.