E-filing is permanently closed for 2021 returns. The only way to file a 2021 return is by mail. If the IRS did not receive your return you can print it, sign and date it in ink, and mail it in. Use a mailing service with tracking like certified mail so you will know they received it.
When you are in a situation where someone else has claimed your dependent before you e-file, filing by mail is your only option. The IRS will not accept an e-file with a SSN that has already been used on another return by someone who claimed that dependent. They will sort it out after you mail your own return claiming your son. Expect a letter at some point in the future and be ready to show the IRS that your child lived with you.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
