Update Part-B (vehicle number) and extend the validity of an existing e-way bill via India's NIC e-Way Bill site-to-site API.

Documented steps

1. Obtain your API client identifier and paired API secret through e-way bill portal site-to-site registration (for eligible taxpayers) or via a GSP. The two paths issue non-interchangeable credentials.
2. Authenticate by sending the client identifier, API secret and GSTIN as headers, with a body carrying the portal username, the RSA-encrypted user credential (encrypted with the EWB public key), and an RSA-encrypted 32-character random session key.
3. The response returns a status flag, a UUID auth token, and an encrypted session-key blob. That blob is AES-256/ECB/PKCS7Padding-encrypted with the random session key you generated - decrypt it locally to obtain the working SEK.
4. All subsequent calls go to POST <URL>/ewayapi/ carrying the client identifier, API secret, Gstin and Authtoken as headers, with a body of {action, data} where data is base64(AES(SEK, payload)).
5. Update Part-B: action=VEHEWB with payload {ewbNo (12 digits), vehicleNo (7-15 chars), fromPlace, fromState, reasonCode, reasonRem, transDocNo, transDocDate (dd/mm/yyyy), transMode, vehicleType}.
6. Extend validity: action=EXTENDVALIDITY with payload {ewbNo, vehicleNo, fromPlace, fromState, remainingDistance, transDocNo, transDocDate, transMode, extnRsnCode, extnRemarks, fromPincode, consignmentStatus (T/M), transitType (R/W/O/blank), addressLine1-3}.
7. Extension is permitted ONLY between 8 hours before the e-way bill's expiry time and 8 hours after it.
8. Only the currently assigned transporter may extend validity or update Part-B; if no transporter is assigned, the generator may do so.
9. Parse the response: status 1/0 plus encrypted data (vehUpdDate and validUpto for Part-B; ewayBillNo, updatedDate and validUpto for extension), or an error object carrying errorCodes.
10. Official docs: https://docs.ewaybillgst.gov.in/apidocs/version1.03/vehicle-number-update.html | https://docs.ewaybillgst.gov.in/apidocs/version1.03/extend-validity.html | https://docs.ewaybillgst.gov.in/apidocs/version1.03/authentication.html