Verifying $0.05 USDC Payments On-Chain in 40 Lines of Python — No Stripe, No SDK, No KYC

Last week I wrote about the French voiceover API that only accepts payment from robots . Today: the part people actually asked me about — how do you verify a $0.05 payment on-chain with zero payment processor, zero SDK, and zero KYC? The answer: one Python function, ~40 lines, stdlib only. Here's the real production code. The setup My endpoint sells French neural TTS voiceovers for $0.03–0.05 USDC. At that price, Stripe is a non-starter (their floor is ~$0.50 per charge) and any processor's KYC kills the "robots welcome" model. So payments go through the x402 pattern: client pays USDC on Base, sends me the transaction hash, I verify it myself against a public RPC before delivering. The verification function import json , os , urllib . request WALLET_BASE = " 0x3f97...D074 " # where I receive USDC_BASE = " 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 " # USDC on Base BASE_RPC = " https://mainnet.base.org " TRANSFER_TOPIC = " 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef " def rpc ( method , params ): req = urllib . request . Request ( BASE_RPC , data = json . dumps ({ " jsonrpc " : " 2.0 " , " id " : 1 , " method " : method , " params " : params }). encode (), headers = { " Content-Type " : " application/json " }) with urllib . request . urlopen ( req , timeout = 30 ) as r : return json . load ( r ). get ( " result " ) def verify_payment ( tx_hash , min_usdc ): # 1. format sanity if not tx_hash . startswith ( " 0x " ) or len ( tx_hash ) != 66 : return False , " bad hash format " # 2. anti-replay: one hash = one delivery if tx_hash . lower () in load_used_txs (): return False , " tx already used (replay) " # 3. fetch the receipt receipt = rpc ( " eth_getTransactionReceipt " , [ tx_hash ]) if not receipt : return False , " tx not found on Base " if receipt . get ( " status " ) != " 0x1 " : return False , " tx failed on-chain " # 4. scan logs for a USDC Transfer TO my wallet want_to = WALLET_BASE . lower (). replace ( " 0x " , "" ) for log in receipt