If your Tax Return was rejected due to missing IP PIN, is because the IRS issued an Identity Protection PIN to you. In order to file electronically, you will need this PIN. You should have received a letter from the IRS with the PIN included. If you didn't receive the letter, you can create an account in the IRS website (if you don't have one) to retrieve it. See the link below
Get an identity protection PIN (IP PIN)
If you have any issues logging in, creating an account or retrieving your PIN, you will need to contact the IRS directly or mail your return. You don't need the PIN number to send your taxes by paper.
Contact the IRS