MoonPay may not be available in certain regions.
If you are using the Uniswap web app, and you are unable to select the "Buy Crypto" Button, your region may not be supported just yet. You can check if your region is supported by MoonPay here.
If you would like to use Uniswap to swap crypto, you can still do so without using MoonPay. To learn more, visit the help center article How to Swap Tokens.