if you received a rejection e-mail, that means someone already filed a return using the same SSN as your dependent. once this happens, you are blocked from e-filing as long as you claim the dependent. you did not provide enough info for us to advise you as to whether you are entitled to claim them but see below for qualifying child or relative (dependent)
you are entitled to claim him/her if he/she is your qualifying child or relative
he/she is qualifying child if all these tests are met
• he/she has the same principal abode as you for more than ½ the tax year. Temporary absences like for school are ignored
• If not a full-time student, under 19 at the end of the tax year. If a full-time student under 24 at end of the tax year.
• he/she hasn't provided over ½ his/her own support
• he/she didn't file a joint return unless there was no tax liability but merely filing jointly to facilitate refund of taxes withheld or estimates paid
or as he/she could be a qualifying relative if all these tests are met
• his/her gross income for 2020 less than $4,300
• you provided over ½ his/her support
• he/she isn't a qualifying child of another taxpayer
