Need a Simple Script coded working with APIs (Price Negotiable)

Need a script coded that works like this: User enters their Instagram username and hits confirm button. The script checks if that user's profile is private or not. If private, create a small error and show it on the screen. If not private, fetch the user's Picture and display alongside the text field for username. User selects a service from the drop down on the same page and the pricing updates accordingly. The page also contains a field for adding coupon codes for discounts. User then clicks the Pay button and is redirected to PayPal for the payment of the amount shown on the page. Once the payment is done, a POST API is called on another site and the same service is ordered on that site. Once the order is placed on that site, the order ID is fetched from that site and is shown to the user. If the payment fails, an error is shown to the user accordingly. If the payment goes through but the order is not placed on the other site through the API call, then a refund is issued/an error is created for me (with enough information) so I can refund the user. All of it needs to be done on the same script/page. Contact me for more details on the project and to know more about the other site I am talking about. I basically want a script to resell some service offered by another site.