I think 8812 is part of the checking process. It is my understanding that it was designed to verify the requirements for the ACTC. For example, dependents that are claimed in alternate years would cause that somebody will have to return the credit, also if the taxpayer earned more money in 2021 than in 2020 over the credit's limit, it will also be affected. Congress asked the IRS to look for a way to avoid double-dipping. That is what I understood from this law. Thanks.