While we always work to secure the best price possible from our liquidity providers, crypto prices can often vary between our partners. In addition to this, cryptocurrencies regularly experience price fluctuations, so there is a small chance you see a different price reflected in your transaction between the time it was created, and the time you see the assets in your wallet.
The order is executed once your card has been successfully charged and MoonPay is satisfied that all compliance requirements have been met. The price can both increase and decrease between the initial purchase request and the point at which MoonPay executes the order.
Apart from the above it is possible that the amount you're looking at in your wallet is a fiat currency equivalent of your cryptocurrency balance (a common practice for wallet providers to display potential value of your cryptocurrency stored). Please, double check the amount of cryptocurrency you ordered with the amount of cryptocurrency you received in your wallet (the fiat equivalent displayed in your wallet is usually the approximate estimation of a potential sell transaction).