In the past my ex-wife has claimed my son but he lived with me the entire year of 2025. When I try to claim him on my taxes as a dependent it says I cannot claim him/

[xmasbaby0]

You probably answered something incorrectly in MY INFO.   Go back to MY INFO and go through all of the interview questions carefully and slowly.  Read every screen top to bottom.

Make sure you have entered your child as a dependent in My Info, and that you have entered the child's Social Security number.    Careful— do not say that your child’s SSN is not valid for employment.  If your child was born in 2025 make sure you said he lived with you the whole year.  There is an oddly worded question that asks if the child paid over half their own support.  Say NO to that question.