Your route quotes differ by $1? Check the source approval first

A missing ERC-20 allowance adds one source-chain transaction, and that gas can make a higher-output bridge quote cheaper overall. For a transfer you need to make now, compare each route after the source approval it actually requires, not just the quoted destination amount.

Check the allowance for the exact source token and spender in each route.
Add any approval transaction’s gas to that route’s cost.
Requote after approval; a changed route may need a different spender.

An existing allowance can make a route cheapest

If your wallet has enough allowance for a route’s spender, you can usually submit the transfer without a separate approval transaction. Under ERC-20, the allowance belongs to a specific owner, token contract and spender; it is not shared across tokens with the same symbol or across bridge providers.

For each quote, check the source token address, spender address and required amount. A balance can cover the transfer while the allowance falls short. If a route’s spender has approval for 100 tokens but the transfer requires 120, expect another approval step; an approval for a different router does not help.

This option is best when the existing allowance covers the input and the route still meets your minimum output and timing needs. It does not fit when a provider rotates its spender, you are using a different token contract, or the allowance is too small. An old approval is not proof that the current quote can execute.

A new approval can erase a quote’s price advantage

If no suitable allowance exists, the token contract needs an on-chain approve(spender, amount) before the route can call transferFrom. That approval costs gas on the source chain, in addition to the transfer’s own gas; if the token requires an allowance reset to zero before setting a new value, there may be two approval transactions.

Compare routes using the same input amount and a common value for source gas and destination output: net value is quoted output minus bridge and swap fees, source transfer gas, and any required approval gas. For example, if route A yields $1 more but its missing approval costs $1.40 at the current gas price, route B is cheaper for this transfer. Use the wallet’s simulated gas estimate and current source-chain fee, not a fixed approval fee: token code, chain and congestion change the cost.

A precise approval limits the spender to the intended amount, but a later, larger transfer may require another approval. An unlimited allowance can avoid repeat transactions for that spender, but leaves that contract permission to pull more tokens later. I’d use an exact amount for a one-off transfer; I’d consider a larger allowance only for a trusted spender I expect to reuse.

A permit helps only when the route supports it

A permit can replace the separate approval transaction with a signature, but only if the token and route support the relevant permit flow. EIP-2612, for example, signs an allowance update with a nonce and deadline; the route must submit that signature on-chain, so execution still uses gas.

This is best when the quote explicitly offers a permit flow and combining authorization with execution saves a transaction or avoids needing source-chain gas for approval alone. It does not fit tokens without compatible permit support, expired signatures, or routes whose spender differs from the one in the signed data. A signature is not a universal allowance: check its token, spender, amount and deadline before signing.

For a transfer through Super Bridge, I’d first compare the routes’ required spenders and existing allowances, then add any approval cost before choosing. That keeps the decision tied to the transaction you can execute now; how Super Bridge compares routes helps frame that choice against your output and timing needs. Before acting, ask yourself: does the cheapest quote remain cheapest after the approval my wallet will actually send?