I am claiming my child this year. My boyfriend (name removed) put on his tax forms that he's not claiming said child. I filed first and I was denied. Why?

When two parents live together unmarried and share custody, only one parent can claim the dependent and all the tax benefits, and the other parent should not even list the child on their tax return.  There is a way to "split" the dependent benefits when parents live apart and share custody (whether divorced, separated or never married) but these special rules don't apply to unmarried parents living together.

Unfortunately Turbotax is not clear on this. When your boyfriend entered your child's name and indicated that you had a custody agreement, and that you were claiming the child, the interview assumed that you were living apart. It gave your boyfriend certain of the split tax benefits of a dependent.  He needed to say "no", there was no agreement to share custody (because that question only applies to legal court orders for divorced or separated parents) or even better, he should not have listed the child at all.

If you have decided that you will claim the child, you should print your return and mail it in.  After your boyfriend's tax return is accepted and his refund paid, he needs to file an amended return to completely delete the dependent from his tax return.  He will also have to repay any EIC or other tax benefits he claimed, including head of household status.

If you were rejected with code F1040-506-01, indicating that some else has claimed your child, then you need to ask your relatives who might have claimed the child. There are tie-breaker rules governing who has the higher right (see below). If you have the higher right, then you should ask the culprit to file an amended return, omitting your child.

https://www.eitc.irs.gov/EITC-Central/abouteitc/basic-qualifications/tiebreaker

If none of your relatives or friends claimed the child, then you may be a victim of identity theft. If this is the case, you should immediately file form 14039. See more information below.

https://turbotax.intuit.com/tax-tools/tax-tips/General-Tax-Tips/Identity-Theft--What-to-Do-if-Someon...

To get your return accepted by the IRS, you will need to file by mail. If you prepared Form 14039, you should include a copy of the form plus the identification documents you included when you initially notified the IRS. You will be required to produce documents to support your claim to the dependent, but do not send these until requested by the IRS.