If client really did not receive the payment, you can do a trace.  This has the tracing information, though is out of date on how to check online to see if client received payment.  The CTC portal is no longer running, so a check to their transcript or to their online irs.gov account, should suffice.   https://www.taxpayeradvocate.irs.gov/news/tas-tax-tip-did-you-have-an-advance-payment-of-the-child-t...