# Step 5 — API

Provide **RPC and explorer** details to Ledger. Use **rpc-explorer-config.ts**:

- **RPC_ENDPOINTS** — Public HTTPS and WSS URLs for Chain 138.
- **EXPLORER** — Blockscout at https://explorer.d-bis.org (EIP3091); optional apiUrl for indexer.
- **BLOCK_AVG_TIME_SEC** — ~2s for Chain 138 (Besu QBFT).

Ledger may run their own indexer or proxy; they will specify. Have these values ready for their config or env (e.g. `API_DEFI_ORACLE_META_NODE`).