Cancel an already-generated GST e-invoice IRN within the statutory 24-hour window, or fetch IRN details by document number, via India's NIC e-Invoice (IRP) API.

Documented steps

1. Generate a 32-character random AppKey. RSA-encrypt both the AppKey and the user password with the e-Invoice system's published public key.
2. Authenticate: POST <base>/api/auth with headers client_id and client_secret, body {UserName, Password (RSA-encrypted), AppKey (RSA-encrypted), ForceRefreshAccessToken}.
3. On success you receive AuthToken, Sek, ClientId and TokenExpiry. Sek is the session encryption key, itself AES-256/ECB/PKCS7Padding-encrypted using your AppKey.
4. Decrypt Sek locally with your AppKey to obtain the raw SEK. Use SEK to AES-encrypt every subsequent request Data payload and decrypt every response Data payload.
5. To cancel: POST <base>/api/Cancel with headers client_id, client_secret, GSTIN, Username, AuthToken and body {Data: base64(AES(SEK, {Irn, CnlRsn, CnlRem}))}.
6. CnlRsn values: 1 = Duplicate, 2 = Data entry mistake, 3 = Order cancelled, 4 = Others. CnlRem is a free-text remark of 100 characters or fewer.
7. Cancellation succeeds only within 24 hours of IRN generation AND only if no active e-way bill exists against that IRN.
8. A successful response returns Status=1 with encrypted Data containing {Irn, CancelDate}. Failures return Status=0 with a base64 ErrorDetails array of {ErrorCode, ErrorMessage}.
9. To look up by document rather than IRN, call the Get IRN Details by Document Details action supplying supplier GSTIN, document type, document number and document date; decrypt the response with SEK as above.
10. Note the retention rule: plain Get IRN details (by IRN) are retrievable for 3 days from generation. GetIrnByDocDetails was introduced in Nov 2020 for the equivalent document-number lookup.
11. Official docs: https://einv-apisandbox.nic.in/version1.03/cancel-irn.html | https://einv-apisandbox.nic.in/version1.03/authentication.html | https://einv-apisandbox.nic.in/release-notes.html