Why Your First Wallet Swap Takes Two Transactions

Your first swap of an ERC-20 token often takes two on-chain transactions: one to let a swap contract use the token, and another to make the trade. The first transaction is an approval, not a purchase. Knowing the difference helps you understand why the wallet asks you to sign twice and what each prompt means.

Why does a wallet ask for approval first?

A swap contract needs permission to move the tokens it will trade on your behalf. ERC-20 tokens use an allowance, a recorded limit on how much a specific contract can take from your wallet. The approval transaction sets that limit; the swap transaction then uses the allowance to exchange your tokens.

That first signature does not send tokens to the pool or guarantee a trade. It records permission on the blockchain, and you usually pay a network fee for it. The later swap is a separate transaction, with its own fee and result. For a venue-specific explanation, read about Blackhole Swap pool types and stuck trades. The pool and routing details can help explain what happens after approval.

This two-step flow is common when a wallet sends a token to a decentralized exchange contract. It is not universal: swapping a network’s native currency usually needs no token allowance, and some services can use a signature-based approval method to combine steps. The wallet may also show one confirmation if you already approved the token earlier.

Does approval happen every time?

No, an approval usually remains in place until it is used up or changed. If the existing allowance covers the trade and the same contract is handling it, the wallet can go straight to the swap. A different contract may need its own approval, even if it belongs to the same exchange.

The amount you approve affects how often you repeat this step. An exact approval limits permission to the planned amount, but another trade may need another approval. A larger or unlimited allowance saves repeat transactions, but gives that contract permission to take more of the token later. You can review and revoke allowances with wallet tools, though revoking permission is itself an on-chain transaction and may cost a fee.

What should you check before signing?

Check the approval prompt before you sign it, then review the trade prompt separately. The approval is permission; the swap is the action that exchanges your assets. A quick check of the token, contract, amount, and trade terms can prevent a mistaken signature.

• Confirm the token and the contract named in the approval prompt.
• Check whether the allowance is limited to the trade amount or is much larger.
• Review the swap’s input, expected output, and slippage—the price movement the trade will tolerate.
• Expect a separate fee and confirmation for each on-chain transaction.

If the prompts do not match the trade you intended, stop and check the wallet details before signing. Once the approval is recorded, the swap still needs its own confirmation; approving a token does not mean the trade has happened.