Find the spender behind an Arbitrum ERC-20 bridge deposit
A user can approve a router address and still fail to deposit through the standard Arbitrum token bridge. The contract that routes a message and the contract that pulls tokens can be different.
Resolve the gateway for this token
On the parent chain, query the configured gateway router for the parent token’s effective gateway. For a standard deposit, inspect the ERC-20 allowance from the sender to the gateway that escrows the tokens and compare it with the intended amount.
user → L1 gateway router → token-specific gateway → escrow
If the router allowance is 100 units but the escrow gateway allowance is zero, that router approval does not authorize the standard gateway’s transferFrom. Verify the exact parent token and chain before requesting any new approval.
Account for custom gateway behavior
Custom gateways can implement different flows, and old custom gateways may not support newer router entry points. Check the token’s resolved route and deployment interface. A successful parent deposit still requires child-side finalization before the bridged balance appears. docs.arbitrum.io Arbitrum documentation