The Goods and Services Tax Network ("GSTN") has enabled the functionality to find the Invoice Reference Number ("IRN") through the Document Number if you forgot to save IRN for any Invoice / Credit Note / Debit Note now you can find it by navigating → Dashboard (https://einvoice.gst.gov.in/einvoice/dashboard) → Search/Enable → Search IRNs (https://einvoice.gst.gov.in/einvoice/search-irn).