Executing a Fill

Once you have received quotes and selected the best one, fill execution is a two-step on-chain process: approve the token spend, then submit the fill transaction. Settlement is atomic — either the full trade completes or it reverts with no partial execution.

Fill Flow

Select a quote

Click on the quote card you want to fill. Only quotes with a valid signature and a non-expired countdown can be selected. The selected card receives a blue highlight and a “Selected” indicator.

After selection, the Execute Trade panel appears showing:

You Pay — the amountIn in Token In.
You Receive — the amountOut in Token Out.
Constraint — for Exact In, the minimum output (minOut); for Exact Out, the maximum input (maxIn). These are enforced on-chain and protect you from unfavourable execution.

Verify the signature

Before the fill buttons activate, the UI runs an asynchronous signature verification:

Calls getQuoteHash(quote) on the RFQ settlement contract to compute the expected hash.
Recovers the signer from the quote’s signature using EIP-191 recovery.
Confirms the recovered signer matches quote.maker.

While verification is in progress, a spinner and “Verifying quote signature…” message are shown. Once verified, a green “Signature verified — maker 0xAbCd confirmed” banner appears and the action buttons become active.

If signature verification fails, the fill buttons are permanently disabled for that quote. You will see “Filling is disabled — this quote has an invalid signature.” Select a different quote to proceed.

Approve the token (Step 1)

If the RFQ settlement contract does not already have an ERC-20 allowance for your Token In, you must approve it first. Click Approve to submit an approve() transaction granting the contract permission to spend your tokens.

The approval step displays:

A numbered circle (Step 1) that animates while the transaction is pending.
A green checkmark once the approval transaction is confirmed on-chain.
The approval transaction hash, linked to the HyperEVM block explorer.

If the contract already has sufficient allowance (e.g. from a previous trade with the same token), this step is automatically marked as complete and you can proceed directly to the fill.

Fill the quote (Step 2)

Click Fill Quote to submit the settlement transaction. This calls the contract’s fillQuote() function, which:

Verifies the maker’s EIP-712/EIP-191 signature on-chain.
Checks that the quote has not expired (block.timestamp <= quote.expiry).
Checks the nonce to prevent replay.
Transfers amountIn (minus the protocol fee) from taker to maker.
Transfers amountOut from maker to taker.
All transfers happen atomically in a single transaction.

Gas is paid by the taker. There is no gas cost for the maker at settlement time — the maker only signed a message off-chain.

Execution Panel States

The execution panel moves through a series of states:

State	UI	Description
`idle`	”Select a quote to execute”	No quote selected yet
`approving`	Step 1 spinner, “Waiting for approval…”	Approval transaction pending
`approved`	Step 1 green check, “Token approved”	Allowance confirmed, ready to fill
`filling`	Step 2 spinner, “Confirming transaction…”	Fill transaction pending
`success`	Green banner, “Trade Executed Successfully”	Fill confirmed on-chain
`error`	Red error box with message	Transaction reverted or failed

Success State

When the fill confirms, the panel displays:

A success banner with the final You Paid / You Received summary.
A Price Improvement callout if the RFQ beat the best venue (e.g. “+12.5 bps better than best venue”).
A prominent “View Transaction” link to the HyperEVM block explorer.
A “New Trade” button to reset the interface and start another RFQ.

Error Handling

If the fill transaction reverts, the error message from the contract is displayed in a red alert box. Common reasons for revert:

Quote expired — block.timestamp exceeded quote.expiry. The UI also blocks fill attempts client-side when the countdown expires, but network delays can cause on-chain expiry even if the UI shows time remaining.
Nonce already used — the maker’s nonce was consumed by a different fill. This typically means another taker filled the same quote first.
Insufficient balance — the maker does not hold enough of the output token to fulfil the quote.
Allowance too low — the taker’s approval was insufficient. Re-approve with a higher amount.

Expiry Protection

The execution panel includes a live countdown that mirrors the quote card timer. If the quote expires while you are on the execution panel:

The fill button changes to “Expired” with a destructive (red) style and becomes disabled.
A red banner reads “Quote has expired — select a new quote to continue.”
The panel border turns red to draw attention to the expiry.

This prevents wasted gas from submitting a transaction that would inevitably revert.