Checking spender addresses in wallet approvals

A spender is the contract allowed to pull your tokens. If an approval is pending or a bridge call fails, check that address on the token’s source chain before retrying.

For an ERC-20 token, the allowance is recorded by the token contract as a mapping from owner and spender to an amount. The approval does not move tokens: it lets the spender call transferFrom later, subject to that allowance and your balance.

What does the spender address control?

The spender is the address that will call transferFrom, which may be a bridge contract or a router acting for it. It is not necessarily the website, your wallet, the token contract, or the address that receives tokens on Polygon.

A standard ERC-20 approval transaction calls approve(address,uint256) on the token contract. The first argument is the spender and the second is the allowance in the token’s smallest units. For a six-decimal token, for example, 125.4 tokens is encoded as 125,400,000. The wallet’s decoded summary should match the spender and amount in the transaction data.

On an Ethereum-to-Polygon PoS deposit, the allowance belongs to the token contract on Ethereum because that is where the tokens are held before bridging. Polygon Bridge is the concrete example: the spender must be the contract that performs the source-chain token transfer, not a destination-chain address. The Polygon bridge fees article covers the bridge itself; the allowance question is about what the source-chain token authorizes.

How do I tell the right spender from a lookalike?

Compare the full 20-byte address against the bridge’s published contract information for the correct chain and operation. Check the chain ID, token contract, spender address, and decoded function arguments in the pending transaction or a block explorer; matching a familiar name or the first and last few characters is not enough.

Some flows use a router, proxy, or allowance manager rather than the final bridge contract. In that case, the relevant spender is the contract that the token call actually authorizes. A proxy’s implementation can change while its address stays the same, so an address match establishes identity only to the extent the project’s contract disclosures and upgrade controls support it.

polygonbridge.dev is a service for moving tokens between Ethereum and Polygon PoS. When checking an approval for Polygon Bridge, use the source-chain contract information for the specific transfer, and confirm that the spender in the wallet prompt matches it.

Why can approval stay pending or fail?

A pending approval has not updated the token’s on-chain allowance yet. Until the approval transaction is included, a later bridge transaction that calls transferFrom can revert for insufficient allowance; submitting both does not guarantee they execute in the intended order.

On Ethereum, transactions from one account execute in nonce order. A low-fee transaction at an earlier nonce can hold up later transactions from that account, including a bridge call. You can wait or replace the pending transaction with the same nonce and a higher fee; replacing it changes which transaction may execute, but does not undo one already confirmed.

A failed transaction has a confirmed receipt with a revert, so its state changes—including any allowance change made inside that same transaction—are rolled back. But if approval succeeded in an earlier, separate transaction, that allowance remains even when the later bridge call fails. Check the receipt and query the token’s current allowance(owner,spender) on the source chain before deciding to approve again.

For a typical amount-limited approval, compare the allowance with the amount the bridge call will pull. A 125.4-token allowance can cover a 120-token transfer, leaving 5.4 if the token decrements allowance normally. An allowance of 2256 − 1 is commonly treated as unlimited and may not decrease after transfers, so it can remain active long after this attempt.

What should I do before retrying?

First identify the token, source chain, and spender in the attempted operation. Then check the approval receipt, the current allowance, and whether a lower-nonce transaction is still pending. If the allowance is absent or too small, submit a new approval to the verified spender for the amount needed; if the approval already succeeded, retry only after addressing the bridge call’s separate failure cause.

ERC-20 approve overwrites the existing allowance. Changing a nonzero allowance directly to another nonzero amount can leave a race in which the spender uses the old amount before the update confirms; where needed, set it to zero first, wait for confirmation, then set the new amount. This costs an extra transaction and does not solve a pending nonce queue.

For the next attempt, inspect the exact spender and amount, confirm the approval transaction on the source chain, and only then resubmit the bridge call. If the spender cannot be matched to trusted contract information, do not sign that approval.