<h1>Business continuity for e-Invoice and e-Waybill systems ensures cross-portal redundancy and unified authentication for uninterrupted filing access.</h1> Advisory sets out redundancy and continuity mechanisms for e Invoice and e Waybill operations: multiple IRPs and dual e Waybill portals as alternate channels; a unified authentication token valid across NIC e Invoice and e Waybill portals; API interoperability enabling cross portal execution of key functions (IRN details, cancellation, e Waybill generation and retrieval, select Part B updates); and a sandbox for testing. Taxpayers are urged to verify direct API cross portal support and coordinate with IRPs, ERPs, GSPs, ASPs and system integrators to enable these redundancies.