If you approve 40 USDC, a bridge contract cannot pull 41 USDC from your wallet. That cap is called a token allowance, and it can explain why a deposit is waiting or failed.
What does the spending limit control?
A token allowance is permission for a specific smart contract—a program on the blockchain—to move a set amount of one token from your wallet. It is separate from your wallet balance: holding 60 USDC does not let a bridge contract use all 60 automatically.
For example, if you approved 25 USDC but try to deposit 60, the contract lacks permission for the extra 35. The deposit may fail, or you may need to approve a higher amount first. Approving tokens is a separate transaction; it does not itself send them to the bridge.
On Polygon Bridge, the approval happens on the network where your tokens currently sit. For a transfer from Ethereum to Polygon PoS, that means approving the relevant token on Ethereum. The Polygon Bridge connection is the concrete case: the allowance must cover the token amount the bridge is asked to move.
Why is the deposit pending or failed?
A pending approval has not yet taken effect, so a deposit that runs before it confirms can fail. A pending deposit is different: it is already submitted, and its status must be checked on the source network before you decide what to do.
Say MetaMask shows an attempted 60 USDC deposit, while the last confirmed allowance was 25 USDC. Check whether an approval transaction is still pending, then check the deposit transaction’s status. If the approval failed, or the confirmed allowance remains too low, approve enough for the intended amount and submit the deposit again only after that approval confirms.
Gas is the network fee paid to process a transaction. An approval and a deposit can each need gas, so a low balance of the source network’s gas token can leave either transaction pending or cause it to fail. Native ETH itself does not use an ERC-20 allowance, though a bridge transfer can still require gas.
What should you check before retrying?
Compare three things: the token balance, the confirmed allowance, and the amount you intend to deposit. If the allowance is short, increase it only enough for your plan; a larger allowance may be convenient later, but gives the contract permission to move more.
Before approving, verify that the token and spender—the contract receiving permission—match the bridge transaction you intended. If the deposit already succeeded, do not submit it again just because the wallet view looks stale; confirm its transaction status first. Ask yourself: is the confirmed allowance enough for this deposit, and has any earlier transaction finished?
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