The Complete Redbelly EligibilitySDK Integration Guide: Widget to Backend to On-Chain

The Redbelly Network EligibilitySDK is the compliance backbone for any dApp that needs to verify user eligibility (KYC, KYB, investor accreditation) before letting a wallet in. The official documentation covers each piece well on its own reference page, but there is no single walkthrough connecting the frontend widget to the backend verifier to the on-chain permission check to a production deployment. This guide is that walkthrough. Everything here was verified against the live documentation at https://docs.redbelly.network/ in July 2026: contract addresses, route names, config fields, issuer DIDs and every error string in the reference section. Every code example was then compiled against the published SDK package (v0.0.31) on React 19 with Vite and on Next.js 16 with the App Router, and the backend verifier was booted and exercised for real. Where the docs and reality diverge (a quickstart repo that is not publicly visible, a credential faucet still under development, three undocumented behaviours the builds surfaced), the guide says so and gives you the workaround. What you will build, in order: A mental model of the two verification mechanisms (and why conflating them costs you a day) A working backend verifier with the three routes the widget demands A plain React integration with full loading and error states A production-grade Next.js App Router setup: secure proxy, SIWE sessions, request gating, and both static and dynamic rendering approaches An end-to-end test run on Redbelly Testnet The decision logic for choosing between the three SDK flows, and the pattern for combining them A complete error reference: every documented error, its cause, and its fix A developer following this guide should have the widget running inside an existing dApp within about four hours. 1. Overview and Architecture What the EligibilitySDK actually is The Redbelly "Onboarding and Eligibility Kit" ( @redbellynetwork/eligibility-sdk ) is a set of React components and hooks for provin