In a move to enhance consistency and reduce duplication in e-invoicing, the Invoice Registration Portal (IRP) will treat invoice or document numbers as case-insensitive for the purpose of IRN (Invoice Reference Number) generation, starting June 1, 2025. This change has been officially notified by the Goods and Services Tax Network (GSTN).

Official Text of the Advisory is as follows
This is to inform you that, effective 1st June 2025, the IRP (Invoice Reporting Portal) would treat invoice/document numbers as case-insensitive for the purpose of IRN generation.
To ensure consistency and avoid duplication, invoice numbers reported in any format (e.g., "abc", "ABC", or "Abc") would be automatically converted to uppercase before IRN generation. This change aligns with the treatment of invoice numbers in GSTR-1, which already treats them as case-insensitive.
The same is shared for your kind information please. For any further clarification, please reach out to the GST helpdesk.