Why does the IRS WMR website show the reference number 9001

[MaryK4]

IRS Reference Number 9001 on the "Where's My Refund" (WMR) tool usually indicates a temporary systemic error or that an incorrect Social Security Number (SSN) or Taxpayer Identification Number (TIN) was entered. It often appears when checking status for a joint return using the secondary filer's info, or when the system needs to verify your identity.