Basics

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Supported payment methods

Payment methods

B402 supports three payment methods based on EIP-712 off-chain authorization:

Method	Description	Token Support
eip3009	EIP-3009 native transferWithAuthorization. No prior approval needed.	U and USD1 only
permit2-exact	Permit2 exact-amount transfer. Transfers the precise amount specified.	Any ERC-20
permit2-upto	Permit2 up-to-amount transfer. Authorizes up to a maximum amount.	Any ERC-20

*For permit2-exact and permit2-upto, the buyer must complete a one-time token approval to the Permit2 contract before the first payment. This approval only needs to be done once per token.

Supported networks

Network	CAIP-2 Identifier	Chain ID	Status
BNB Smart Chain Mainnet	eip155:56	56	Live (access on request)
BNB Smart Chain Testnet	eip155:97	97	Live

Supported tokens

Mainnet (eip155:56)

Token	Contract Address	Decimals
U	0xcE24439F2D9C6a2289F741120FE202248B666666	18
USD1	0x8d0D000Ee44948FC98c9B98A4FA4921476f08B0d	18
USDC	0x8AC76a51cc950d9822D68b83fE1Ad97B32Cd580d	18
USDT	0x55d398326f99059fF775485246999027B3197955	18

Note on amount encoding: All paymentRequirements.amount values are atomic units (smallest indivisible token unit), so for an 18-decimal token, $0.01 = 10000000000000000 (1e16), not 10000. Verify against the contract's on-chain decimals() if in doubt — that's the source of truth.

Testnet (eip155:97)

Token	Contract Address	Decimals	Supported Methods	How to Obtain
Mock U	0x330949Aed7d00FCe0558C64ED6FeC9792616cC39	6	eip3009, permit2-exact, permit2-upto	Mint from token contract directly by yourself
USDC	0xEC1C60D64a06896Df296438c12edD14E974FDE47	6	permit2-exact, permit2-upto	Mint from BnbChain faucet
USDT	0x337610d27c682E347C9cD60BD4b3b107C9d34dDd	18	permit2-exact, permit2-upto	Mint from BnbChain faucet

Key contract addresses

Contract	Network	Address
Permit2	BSC Mainnet	0x000000000022D473030F116dDEE9F6B43aC78BA3
Permit2	BSC Testnet	0x000000000022D473030F116dDEE9F6B43aC78BA3

Permit2 buyer prerequisites

Before using permit2-exact or permit2-upto payment methods, the buyer (payer) must:

1. Approve the Permit2 contract — Call the token's approve() function to grant the Permit2 contract an allowance. This is a standard ERC-20 approval and only needs to be done once per token.
2. Sign EIP-712 authorization — For each payment, the buyer signs an off-chain EIP-712 message. No additional on-chain transaction is required from the buyer.

For eip3009 (U, USD1), no prior approval is needed — these tokens natively support transferWithAuthorization.