Payment of child support has nothing to do with having the right to claim a dependent. The custodial parent has the right to claim a dependent child. The IRS defines "custodial parent" as the parent with whom the child spent the greater number of nights during the tax year. The non-custodial parent may not claim the child without a written release from the custodial parent using Form 8332 or equivalent. Sometimes the custodial parent is required to give up their right because of a court order.
Bottom line: Your ex can claim her (assuming she otherwise qualifies to be claimed as his dependent), but you'd have to give him a Form 8332. https://www.irs.gov/uac/form-8332-release-revocation-of-release-of-claim-to-exemption-for-child-by-c...
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
