Wallet Connect and Currency Purchase Modal

I want to create a modal. That modal allow user connect wallet, and buy an off chain currency using erc20 token. There are 2 options of buying. One is input exactly the amount of the off chain currency, and the cost in erc20 token will display by calling an function. The second option is input the amount of erc20 token and the amount of off chain currency that user can get will be display, also by calling a function. Make the modal works with mock function, and the price will update every 3 second when the input have value. Make the UI clean, easy to use, best UX.