Build checkout page PHP

I want a checkout page like https://goread.io/, if users want to buy followrs, then the checkout page has to show a system to enter instagram user and display user photo on screen, in backend It will have to be transformed from username to profile link ex: the user enters the username "messi" this is transformed to www.instagram.com/messi, if the user buys liks or viws for Instagram the user has to enter his username , and the user's Instagram posts must be displayed with the option to choose one, in the backend when selecting a photo the link will be copied and the order will be sent with the script, if the user, on the other hand, wants to buy any other service, the user is sent to the default payment page.