Sorry, late to the party.  Our bourbon friend has already done most of the leg work on this one and you should give Joshua's owner credit for the solution.

The EIP amounts are split between the two taxpayers on an MFJ return.  When you look this up in IRS transcripts you have to look up EACH taxpayer and add the amounts together.

In this case, the first EIP amount was $2,131.95.  The second EIP amount was $1,031.95.  Only half of these amounts were entered into the software resulting in an incorrect RRC.  Your client gave you incorrect information and from that point on it was GIGO.

If we want to check the math, they filed their 2019 tax return early enough that it was available in the IRS system for EIP1 so we don't have to dig up 2018 data.  EIP1 would have been calculated as:  $1,200 + $1,200 + $500 = $2,900 base - $768.05 phase-out = $2,131.95.  The phase out is calculated as $165,361 - $150,000 = $15,361 x 5% = $768.05.

EIP2 would have been calculated as:  $600 + $600 + $600 = $1,800 base - $768.05 phase-out = $1,031.95.

$2,131.95 + $1,031.95 = $3,163.90.

The IRS thinks (and likely they're correct) that they issued $3,163.90 of EIP.  Your RRC calculation only included $1,582 of that.  They fixed it.  The client owes the difference.

Rick