Can someone tell me what to do if my ex claimed our daughter on his returns? She lived with me all of 2023 and he does not provide more than 50% of her living expenses.

Someone else claimed my dependent and my return was rejected

If someone else claimed your dependent already, then your e-filed return will be rejected.  Print, sign and mail your own return which claims your dependent.  Mailed returns are processed differently by the IRS.  It will take some time (maybe even up to a year) but eventually the IRS will contact both parties and sort out who could rightfully claim the dependent.  The person who wrongfully claimed the dependent will face repayment of refund $, plus penalties.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.

If your ex e-filed their tax return and it was accepted by the IRS then you will have to print and mail your tax return claiming your daughter as your dependent.  You will not be able to e-file your tax return.

Within a year the IRS will be sending both of you letters to investigate why the daughter's Social Security number was used on both tax returns as a dependent.

The loser of the investigation must pay back any tax refund based on improperly claiming the child as a dependent plus penalties and interest.

See this TurboTax support FAQ for how to print and mail a tax return when using the online editions - https://ttlc.intuit.com/turbotax-support/en-us/help-article/printers-printing/print-mail-return-turbotax-online/L5bwuqXGy_US_en_US?uid=ls9kbcg6