GSTN informs that from June 01, 2025, Invoice Reporting Portal (IRP) will treat invoice/document numbers as case-insensitive for the purpose of Invoice Reference Number (IRN) Generation; Invoice numbers reported in any format (abc, ABC or Abc) will automatically be converted to uppercase before IRN generation; This development has been made to ensure consistency and to avoid duplication; GSTN further mentions “this change aligns with the treatment of invoice numbers in GSTR-1, which already treats them as case-insensitive”: GSTN Advisory
http://mohansekhar.in/wp-content/uploads/Advisory_on_Case_Sensitivity_in_IRN_Generation.pdf