If you already received a round 3 payment for someone who is not on your 2020 tax return, I don't see any guidance from the IRS on that situation yet. They seems to be focused on pushing the money out rather than posting tips to their web site. I don't see any reason why the rules would be different than for round 1 and 2, which did not have to be paid back. However, if you are concerned, you may want to save the money until the IRS releases more information later this year.
