A token’s return value is the short answer its contract gives after a transfer request. A bridge deposit can fail if that answer is missing or signals failure and the bridge cannot handle it.
The bridge must interpret the token’s answer
Most Ethereum tokens use the ERC-20 standard, a common set of rules for token transfers. Its transfer functions return either “true” for success or “false” for failure, and callers are expected to check that answer.
To deposit tokens, a bridge first needs permission to move them, then asks the token contract to transfer them into bridge custody. On Polygon PoS, the Polygon Bridge locks tokens on Ethereum before a matching token is issued on Polygon; the deposit depends on the token call completing successfully.
Some older tokens return no answer at all, even when a transfer succeeds. A bridge that expects “true” may treat the empty answer as an error and stop. A safer contract pattern, often called SafeERC20, accepts either “true” or no answer, but rejects “false” and failed calls.
A rejected answer can undo the whole deposit
Imagine you approve a bridge to move 100 tokens, then submit a deposit. The token transfers the 100, but returns no value; if the bridge cannot accept that response, the transaction reverts, meaning the chain cancels its changes.
That cancellation also undoes the token transfer, so the bridge should not keep the 100 or issue the Polygon-side tokens. You still spend gas, the network fee for processing the attempt. The exact amount depends on the transaction and network conditions.
For regular transfers, how to choose a Polygon Bridge route covers route selection in more detail. For this issue, check whether the token is supported and whether the chosen bridge can handle its transfer behavior; support for one token does not prove support for every token with similar branding.
Token behavior matters more than its name
Before choosing a route, verify the token’s contract address on the source chain and look for evidence that its transfer works with that bridge. A familiar ticker or a successful wallet balance display does not show what value the token returns to a contract.
One subtle case is a token that returns “true” but transfers less than requested, perhaps because it deducts a transfer fee. The return value alone cannot reveal that shortfall. A bridge may need extra checks, such as comparing its token balance before and after the transfer.
Does a missing return value mean the token transfer failed?
No. Some tokens complete a transfer without returning a value, while others return “true” or “false.” Whether a no-answer token works depends on how the bridge handles the response. If the bridge rejects it, the transaction reverts and the transfer is undone, though the gas spent on the failed attempt is not returned.
Can I tell from a token’s name whether a bridge accepts it?
No. Different tokens can share a name or ticker while using different contracts and transfer rules. Check the exact contract address and whether the chosen route supports that asset. For unusual tokens, a successful small test deposit can provide evidence, but it still costs gas and does not guarantee every later transaction will behave the same way.