b402

Gasless crypto payments on BSC. One line of code.

Install

pip install b402

Fastest Way to Get Started

# 1. Set your private key
export PRIVATE_KEY="0x..."

# 2. Run Python
python3

# 3. One line to pay!
from b402 import pay

result = pay(amount="0.01", token="USD1", recipient="0x...")
# Done! ✨

That's it!

• First payment: Auto-approves $10k cap + sends payment (~5 sec)
• Future payments: Just pays instantly (<3 sec, gasless!)

What Just Happened?

1. Checked if USD1 is approved for B402 relayer
2. Approved $10,000 worth (one-time, costs ~$0.10 gas)
3. Sent your payment
4. Next 1000+ payments will be instant (no approval needed)

Defaults to BSC mainnet. Set network="testnet" for testnet.

Manual Control (Optional)

from b402 import B402

b402 = B402()

# Check approval status
approved, allowance = b402.check_approval("USD1")

# Manual setup if you prefer
if not approved:
    b402.setup("USD1")

# Send payment
result = b402.pay(amount="0.01", token="USD1", recipient="0x...")

How It Works

First Payment:

1. Checks if token has sufficient allowance for this payment
2. If not, automatically approves up to $10,000 worth (costs ~$0.10 gas, one-time)
3. Sends payment

Subsequent Payments:

1. Uses existing allowance ✅
2. Sends payment immediately (gasless!)
3. Re-approves automatically if allowance runs low.

Security

Smart Approval Limits:

• Never approves infinite amounts
• Default cap: $10,000 worth of tokens
• Checks allowance before each payment
• Only approves when needed

safe:

# Approves: $10,000 worth (reasonable limit)
approve(relayer, 10000000000000000000000)  # 10,000 * 10^18

Examples

Simplest (auto-approval):

from b402 import pay

result = pay("0.01", "USD1", "0x...")
# First time: approves + pays
# After that: just pays (gasless)

Disable auto-approval:

result = pay("0.01", "USD1", "0x...", auto_approve=False)
# Will return error if not approved, prompting manual setup

Manual control:

from b402 import B402

b402 = B402()
b402.setup("USD1")  # Explicit one-time setup
result = b402.pay("0.01", "USD1", "0x...")

Run the complete demo: python examples/complete_demo.py

Supported Tokens

Mainnet: USD1, USDT, USDC Testnet: USDT

30-Second Tutorial

# Install
# pip install b402

# Set key
import os
os.environ["PRIVATE_KEY"] = "0x..."

# Pay (that's it!)
from b402 import pay
result = pay("0.01", "USD1", "0x...")

# Check result
print(result.tx_hash if result.success else result.error)

Copy, paste, done. 🚀

API Reference

pay() - Simplest

from b402 import pay

result = pay(
    amount="0.01",           # Amount to send
    token="USD1",            # USD1, USDT, or USDC
    recipient="0x...",       # Recipient address
    network="mainnet",       # Optional: "mainnet" or "testnet"
    auto_approve=True,       # Optional: Auto-approve if needed
    debug=False              # Optional: Show debug logs
)

B402() - Advanced

Create B402 client for manual control. Defaults to mainnet.

b402 = B402()  # mainnet
b402_test = B402(network="testnet")

b402.setup(token)

One-time setup: approve relayer to spend tokens.

result = b402.setup("USD1")
# Returns: {"approved": True, "allowance": int, "tx_hash": "0x..."}

b402.check_approval(token)

Check if token is approved.

approved, allowance = b402.check_approval("USD1")

b402.pay(amount, token, recipient)

Send gasless payment.

result = b402.pay(amount="0.01", token="USD1", recipient="0x...")
# Returns: PaymentResult(success, tx_hash, error, payer, recipient, amount, token)

pay() - One-liner

Factory function for simple usage (after setup).

from b402 import pay

result = pay(amount="0.01", token="USD1", recipient="0x...")

Environment Variables

• PRIVATE_KEY - Required. Your wallet private key (with 0x prefix)

Examples

• examples/complete_demo.py - Full workflow with setup
• examples/one_liner.py - Simplest payment
• examples/check_approval.py - Check approval status

Network Details

BSC Mainnet (Chain ID: 56)

• Relayer: 0xE1C2830d5DDd6B49E9c46EbE03a98Cb44CD8eA5a
• USD1: 0x8d0d000ee44948fc98c9b98a4fa4921476f08b0d
• USDT: 0x55d398326f99059fF775485246999027B3197955
• USDC: 0x8AC76a51cc950d9822D68b83fE1Ad97B32Cd580d

BSC Testnet (Chain ID: 97)

• Relayer: 0x62150F2c3A29fDA8bCf22c0F22Eb17270FCBb78A
• USDT: 0x337610d27c682E347C9cD60BD4b3b107C9d34dDd

License

MIT