Isn't the 2nd stimulus payment based on income for 2019? If this is correct, why is the program using income from 2020 to determine limitation?

Sorry, I found the answer. The Stimulus payment is based on 2019 income but if the 2nd stimulus payment wasn't rec'd the program will base income limitation on 2020 income levels.  If your client hasn't rec'd the 2nd stimulus payment and their income for 2019 was w/in the limitations but not so for 2020, the client / you will need to contact the IRS for instructions on how to get the 2nd stimulus payment

The first and second payments were Advances. The whole point of the 2020 tax return having the fields is that you are reconciling the reality of 2020 against any advanced payouts.

There is no splitting the qualification for the first and second payments against different income limits. They are both part of 2020 tax return computation.

In other words, if they don't qualify in 2020 due to income limitations, but they got any payment for first or second EIP, they got money they were not really entitled to.