Have you verified with client that it's correct?  Waste of time to try previous year's PIN.

Have your clients check this out - there have been IPIN problems in the past.

https://www.irs.gov/identity-theft-fraud-scams/retrieve-your-ip-pin

Paper file

You need to use the IPPIN that was issued to the client in Jan 2024 on ANY returns that are EFiled in 2024..if youre trying to use the IPPIN that was issued in 2023, youre too late to use that, you need the most current one.

If youve double checked that the client is giving you the most recent one and theres no other people on the return that have IPPIns, you may be stuck filing by paper.