Eligibility for the first two payments is the same. It’s based on 2020 filing status, dependency status and adjusted gross income. IRS sent out checks before 2020 returns, so it used 2019 (or in some cases, 2018) information. Some people received payments for which they aren’t eligible, and they generally get to keep them. Some people failed to receive payments for which they are eligible, and they get to claim a refundable credit on their 2020 income tax returns.
Individuals can check on their third payment on the IRS Get My Payment page.
It’s too late to use that page to check on the first two payments. If you’re concerned that the second payment may have been sent but not received, you would need to establish an account with the IRS.
For now, the main thing to know is that there’s a credit on this person can claim on his 2020 return if he was eligible for the second payment but didn’t receive it. If using software to file that return (highly recommended), he’ll see a question about this.