When a SyncSwap swap says insufficient gas even though you hold the token, stop altering slippage: leave a small reserve of the network’s native token, then retry from SyncSwap. In this case, keeping roughly $3 of ETH available fixed the failure in under ten minutes.
When the error says “insufficient gas” but the trade looks affordable
The quote is not your total cost. You can have enough USDC, USDT, or another input token to make the trade and still be unable to submit it because the network charges gas in its native asset. On ZKsync Era, that means ETH; the exchange cannot take gas from the token you are selling.
This was the exact situation: a wallet held 250 USDC on ZKsync Era and attempted to swap it for ETH. The interface produced a valid quote, but the wallet rejected the transaction for insufficient gas. The user had set the amount to the full 250 USDC and had no ETH left on that network.
If the wallet balance shows the token but ETH reads zero or nearly zero
That combination produces a transaction failure before the swap can happen. The required fee may be small, but it must be paid separately and the final amount varies with network conditions and the transaction itself.
- Check that the wallet is connected to the same network as the token balance.
- Look at the native ETH balance, not the dollar value of the token being swapped.
- Leave a buffer instead of funding only the exact displayed fee.
For a small swap, keeping a few dollars’ worth of ETH is usually more useful than trying to estimate the fee to the last cent. You may need one transaction to approve a token for spending and another to execute the swap, so a balance that barely covers one signature can still leave you stranded.
Once ETH is available on the same network, use the quoted route unchanged
The fastest recovery is to return to the SyncSwap swap page, enter a slightly smaller input amount if necessary, and review the quote again. The router can use direct pools, intermediate tokens, and split paths; you do not need to manually force a direct pair merely because the first attempt failed.
- Keep enough ETH for gas before choosing the amount to sell.
- Select the intended input and output tokens by their verified contract or established token listing, not ticker alone.
- Approve the input token only if the wallet requests it.
- Confirm the swap transaction and wait for its on-chain confirmation.
If you are selling ETH itself, the same principle applies in reverse: do not enter your entire ETH balance as the input. Subtract a practical gas reserve first. A “max” button is an amount suggestion, not a guarantee that the next transaction will have enough fee currency left.
Before you raise slippage to make a failed transaction pass
Increasing slippage will not solve a missing-gas problem and can make the result materially worse. Slippage controls how much the execution price may move before the transaction reverts; it does not supply ETH for network fees.
| What you see | What it usually means | What to do |
|---|---|---|
| “Insufficient gas” or wallet cannot estimate fee | No usable native-token balance | Add or retain ETH on that network |
| Quote changes or transaction reverts after signing | Price moved beyond tolerance | Refresh the quote; adjust slippage only deliberately |
| Approval succeeds but swap fails | Gas was enough for approval, not the swap, or the quote moved | Check remaining ETH, then refresh the quote |
After the swap succeeds but the received token seems missing
The asset is normally in the wallet on the network where you traded, even if the wallet does not automatically display it. Confirm the completed transaction in the network explorer, verify the output token contract, then import that exact contract into the wallet if needed. Do not repeat the swap because a wallet’s token list is incomplete.
When you want to avoid paying for this mistake twice
Keep a permanent native-token reserve on every network where you trade, bridge, or claim assets. The costliest error in this case was not the failed transaction itself; it was treating the error as a pricing issue and considering a high-slippage retry. Preserve gas first, diagnose the message literally, and only then revisit the trade settings.