The amount can change because the market moves before the swap finishes. With a wallet swap, the displayed output may be an estimate based on a rate that can change while your payment confirms.
A quote is the estimated exchange rate and destination amount for your swap. In a cross-chain swap, a service receives one asset and arranges for another to reach your compatible wallet. The XMR bridge is one example of a service for swapping Monero (XMR) with tokens on other blockchains.
Some services use a floating rate: the final amount follows the market rate when the swap is processed. The time between sending and processing matters. Monero blocks arrive about every two minutes on average, and a service may wait for several confirmations—blocks added after the one containing your payment—before acting on it.
For example, say 0.5 XMR is quoted at 150 tokens per XMR. That suggests 75 tokens before fees. If the rate moves to 146 before processing, the same amount gives 73 tokens before fees. These figures are illustrative; the actual rate depends on the assets and market at the time.
Two cases show why the result can differ. If the market stays steady while your XMR confirms, the final amount may stay close to the quote. If the market moves during that wait, a floating rate can produce more or fewer tokens.
Fees can also reduce what arrives. A service may include its charge in the exchange rate or show it separately; the destination network may also charge a fee to send the token. Check the estimated amount after charges, rather than comparing only the headline rate. A thin market, with fewer buyers and sellers available, can make a large swap move the rate more.
Wallet ownership does not freeze a price. For instance, you might send XMR from Cake Wallet or Feather Wallet and receive a token at a MetaMask address. The wallets hold or display the assets; the swap service handles the exchange between networks.
Compare the expected amount you will receive, the rate type, and any expiry time shown for the quote. A fixed quote can protect the stated rate for a limited window, while a floating quote can change with the market; the terms depend on the service. If your XMR confirms after a quote expires, the service may use a new rate or follow another stated policy.
Before sending, confirm that the destination wallet supports the exact token and network. Then decide whether the estimated amount is acceptable if the rate shifts during confirmation. In practice, I focus on the net amount and the quote conditions, not the first number displayed.
Takeaway: wallet swaps can change in value while the market moves and your payment confirms.