use-modular-wallets

Register a passkey using toWebAuthnCredential with WebAuthnMode.Register, then call toCircleSmartAccount with the credential wrapped in toWebAuthnAccount. The MSCA deploys lazily on the first outbound transaction, so no upfront deployment gas is needed.

Pass paymaster: true in sendUserOperation to sponsor gas via Circle Gas Station. Encode the USDC transfer with encodeTransfer using parseUnits(value, 6) since USDC has 6 decimals, then wait for confirmation with waitForUserOperationReceipt.

MSCAs are supported on Arbitrum, Avalanche, Base, Monad, Optimism, Polygon, Unichain, and Arc Testnet. They are not available on Ethereum mainnet, Solana, Aptos, or NEAR. Each chain requires a specific path segment appended to the client URL for toModularTransport.

During setup, generate a BIP-39 mnemonic and register its derived EOA as a recovery address on-chain. When the passkey is lost, validate the mnemonic, create a new passkey credential, and call executeRecovery to swap the account owner to the new passkey.

AA21 means the sender did not pay prefund, so verify paymaster: true is set or fund the account with native tokens. Error 155203 occurs when sending a nonzero nonce before the wallet is deployed; send the first user operation with nonce 0 since MSCAs deploy lazily.