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-exactandpermit2-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.amountvalues are atomic units (smallest indivisible token unit), so for an 18-decimal token, $0.01 =10000000000000000(1e16), not10000. Verify against the contract's on-chaindecimals()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:
- 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. - 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.