Here: "Generally, if you were a U.S. citizen or U.S. resident alien during 2021, you were eligible for $1,400 ($2,800 for a joint return), plus $1,400 for each qualifying dependent"

Of course, that prepayment was based on the projection year (2019 or 2020 tax return). That means the one person not claiming the child, and then based on AGI, is qualified for up to $1,400 (having got $700) and the other person claiming the child is qualified for up to $2,800 and got $1,400 (2 X $700).

Potentially.