Fees, and the setting that underfunds orders

Fees matter here for one reason that has nothing to do with cost. A single wallet setting decides whether the amount the order asked for is the amount that arrives.

The setting

Wallets differ on one behaviour. Some treat the figure you type as the total leaving your balance and subtract the network fee from it, so less arrives. Others add the fee on top, so the exact figure arrives. Neither is wrong. Only one funds an order correctly.

The amounts involved are tiny, which is precisely why it catches people. An order sits unfunded over a difference smaller than the rounding on the price, and nothing about the wallet suggests a problem, because the transaction succeeded.

Fee behaviour by coin

Practical rule

Configure the wallet to add the fee on top once, and it stops being something to remember. Failing that, send very slightly more than the requested amount, since a small surplus generally lands on your balance and a small shortfall leaves the order unfunded.

If you already underpaid

Do not send a second payment before asking. Open a support message with the order reference and the exact amount sent. The coin is on the chain and visible, so this is recoverable, and adding a second unmatched payment makes it less so.

Verified addresses

Before you sign in. Open these in Tor Browser only, then compare the onion printed on the login screen against your browser address bar. If they do not match, close the tab.