single webpage with certain functionality for existing website

hi we need a webpage with certain functionality currently, our website is in WordPress so its your convenience to add a page to our website or create a subdomain and make the page in your own scripting language there. our requirement : we have to make promotions for a android app only in 6 states of india and our client have 6 different tracking links for 6 different states. Now our plan is to promote it on social media to users by providing 20 INR mobile topup on install for those particular states only via instagram stories so basic functionality should be when user comes to this page at top there will be banner stating this offer of 20 mobile topup followed by asking them to select the state and enter there mobile number now based on the state selection their link will be available to click and download the app via the button and secondary functionality is passing that mobile number as a suffix to the url for example, state A have www.xyz.com/aff= is link and user input for the mobile number is 12345 then button should redirect him to www.xyz.com/aff=12345 for selecting state a look for webpage should be decent not looking like a spammy page optionally storing those entries would be helpful