`invalid_exact_evm_non_canonical_signature`

The signature is a valid shape but uses the high-s form, which is rejected.


Reported by	the facilitator, during verify
Usually fixed by	the buyer

Cause

A plain ECDSA signature from an ordinary wallet must be in canonical low-s form. Tokens such as USDC reject the other form on-chain.

Fix

Buyer: sign with a standard library such as viem or ethers, which produce canonical signatures. Hand-rolled signing code is the usual cause.

About this reference

Causes are taken from the source of @x402/evm 2.31. Other facilitators and later versions may use the same code for slightly different checks. See all x402 errors.