Diagnose a rejected ERC-2612 permit
Two browser tabs can prepare valid-looking permits for the same owner while competing for one nonce. Inspect the token’s state before requesting another signature.
Compare the signed nonce with contract state
Suppose both tabs read nonces(owner) = 12 and sign different allowances. The first permit succeeds. A new nonces(owner) call now returns 13. Submitting the second signature against this state fails because the contract hashes the current nonce.
nonces(owner): 12 → 13
signed nonce: 12
Read the token’s domain separator and verify the owner, spender, value and deadline in the typed data. The permit authorizes an allowance. An actual token transfer is a separate action.
Retry with the owner’s current intent
Check allowance(owner, spender) before prompting the user again. The desired allowance might already exist. If a fresh permit is needed, rebuild and sign with the current nonce. Editing the nonce inside an existing signature invalidates it. eips.ethereum.org EIP-2612