A first SyncSwap swap of an ERC-20 token usually takes two on-chain transactions: an approval that grants a contract spending permission, then the swap. The approval sets an allowance, a ceiling on how much of that token the contract may take from your wallet. Check that ceiling before you trade; swapping native ETH follows a different path.
What does a SyncSwap approval authorize?
An approval authorizes one spender contract to transfer up to a stated amount of one token from your wallet. It does not send the tokens when you approve. When you later confirm the swap, the contract uses that allowance to take the input token and complete the trade through an automated market maker pool.
A swap and a liquidity deposit are different uses of your tokens, so an approval for one may not cover the other. SyncSwap on zkSync Era trades against pool reserves; providing liquidity means putting assets into a pool. If you decide to deposit after your first trade, SyncSwap liquidity pools let you provide assets to a Classic Pool or Stable Pool. Check any approval requested for that deposit separately.
What should you check before approving?
Match the permission request to the trade you intend to make. These four details tell you what you are authorizing:
- The network and gas balance
- The input token
- The spender contract
- The allowance amount
Network and gas balance. Your wallet must be on the supported layer 2 network where you hold the token. A balance on Ethereum mainnet is separate from a balance on zkSync Era, for example. Keep enough of that network’s gas asset for both the approval and swap unless your wallet explicitly shows another fee arrangement; having plenty of the token you want to sell does not by itself pay transaction fees.
Input token. Approval concerns the token you will spend, not the one you hope to receive. Check its contract address as well as its name or symbol, since different tokens can share a symbol. If you change the input token, expect a different approval request.
Spender contract. This is the address receiving permission, often a trading contract rather than another person’s wallet. Check it against the contract identified by the exchange for your intended action before signing. An earlier approval on another network, or for another spender on the same network, does not authorize this one.
Allowance amount. Read the number as a spending limit, not a prediction of what the swap will cost. An approval for 100 tokens allows the named contract to transfer up to 100; an unlimited approval can cover future trades without another approval transaction. If you abandon the swap after approving, the unused allowance can remain available until you change or revoke it.
How much should you approve?
For a first, one-off trade, I would approve the amount I plan to swap. Say you hold 150 tokens and intend to trade 100: a 100-token allowance is enough for that trade and leaves no permission to spend the other 50. If the trade uses less than 100, the unused part of the allowance may remain, so check it afterward.
A frequent trader faces a different choice. Someone swapping 10 tokens every week might approve a larger amount once and avoid paying for a new approval whenever the remaining allowance runs out. That saves transactions but leaves more tokens accessible to the spender, including tokens added to the wallet later. The deciding factor is how much future access you are comfortable leaving in place, not the size of your current balance.
Some tokens or trading flows can use a signed permit instead of a separate on-chain approval, if both the token and exchange support it. The signature can still grant spending authority, so read its spender, amount and deadline with the same care. If no permit is offered, the ordinary approval transaction is the route to expect. Native ETH itself needs no ERC-20 allowance.
What will the approval and swap cost and take?
A standard first ERC-20 trade has two network fees and two confirmations: one for approval and one for the swap. On an Ethereum layer 2, each fee is often in the cents-to-low-dollars range, but the wallet’s estimate matters more than any fixed figure. For example, a $0.10 approval estimate plus a $0.30 swap estimate means about $0.40 in network fees. Gas demand and the cost of publishing layer 2 data to Ethereum can change those estimates.
Each transaction may confirm in seconds or take a few minutes; wait for the approval to confirm before submitting the swap. The swap has a separate pool trading fee, and a large order relative to pool liquidity can move its execution price. Check the quoted output and minimum received—the least you will accept after your slippage setting—before confirming. The approval fee is still spent if you decide against the swap afterward.
Your next step is to choose the token and amount you want to trade on SyncSwap, then compare the approval’s network, token, spender and allowance with that plan. Approve only after those details match. Once it confirms, review the swap’s estimated fee and minimum received, and confirm the trade.