I have 2 sons with my ex-wife. We have been divorced for several years and file separately. Our agreement is such that each one of use claims one child. However, for the COVID stimulus she already claimed both sons. She says she has not submitted her 2019 taxes. When I try to file my 2019 taxes claiming the son I normally claim, the forms are rejected saying someone has already claimed a dependent with the same SSN. Since she has claimed both sons for the stimulus, could this be the reason my taxes are being rejected? How do I fix this?
You cannot fix it. If you are the one who is supposed to claim the child for 2019, and she has already used his SSN on a return--which it seems she did for the stimulus -- then all you can do is print, sign and mail your own return, and let the IRS sort it out.
You may get the last laugh--because since she already filed for the stimulus -- probably using the non-filer site -- and plans to file an actual tax return, her tax return will be rejected too, and she will have to paper file.
Remember that if you are not the parent where the child lives more than half the nights of the year, you can't claim the child as a dependent unless the other parent gives you a signed form 8332 dependent release. Then in Turbotax, indicate the child lived with you less than half the year, and that you do have a signed form 8332. You will get the child tax credit, but you don't qualify for head of household, or the child care credit, or EIC, because those benefits always stay with the parent where the child lives more nights of the year, and can't be waived, transferred or shared, even by court order. After you e-file, you must mail the original form 8332 to the IRS with a cover page that Turbotax will tell you to print. If you file by mail you must include the original signed 8332.
If you have been claiming your child without form 8332 by saying the child lived with you when they did not, you may be in the wrong, not your ex.
Filing properly with form 8332 sometimes clears an e-file block that is caused by claiming the child lived with you when it did not. But in this case, the e-file block might also be caused if your ex filed a "non-filer" return.