Is there an issue where proof is needed? EDIT: you said "The IRS doesn't have a record of the payroll taxes for 2022 for my client"

Your client should get payroll reports for every pay period and a year end summary, along with W-2s.

The PEO files payroll tax returns with a schedule listing each individual company and EIN, I believe. It took a while but I was able to get some of these in the COVID/PPP days.