WHMCS API oder form on stadalone php file

Here is full project description in details on what is needed. Custom Order Form for WHMCS billing system, must use PHP, AJAX, Javascript. The custom order form needs to have from 3-8 steps. (Must work as a php shopping cart and display the content of the cart along with the total price) Step 1. Display packages that are in the 2 WHMCS Group (Our Internal Product | Our Services). (We only display the two groups products in step 1) For the "Our Internal Product" Group When the client select a package we should also define the custom fields and pass it via the sign up because a specific custom field launches automatic WP install. For the "Our Services" The service product does not need step 2,3, 4 and 5, it bypass and goes to step 6. Our service is for client to buy a service like: Install a SEO plugin, Update the logo etc. One step 6 the client is asked to login in, the register is not asked as the services are only able to purchase if they have bought a hosting with already. if the client is trying to login with an account that does not exist. that we inform with alert saying : this account does not exsits, either click forgot password or to buy this service you can only if you have purchased a hosting package with use. Step 2. Display 3 options : Register a domain, Use existing Domain, register under a subdomain [login to view URL] If the user selects to register a domain, than Must check the domain's availability by connecting to WHMCS using API's and return a true or false value. if true : must show other available TLD's if faults : must show other available TLD's. Provide option to domain add ons, such as "make private registration" and automatically add the additional charge to the total in real time. If the user select register the domain or subdomain that it has a cost this servers and must update the total price and the content of the shopping cart in real time. Step 3. SSL certificates ( only for new registered domain or domain transfer) Step 4. Show additional products which will be previously configured in WHMCS, such as "Design Facelift", "Exclusive Tech support", "Guaranteed Backups" etc The additional products will only be shown the products that we have assigned to a specific group in the WHMCS system. ( In WHMCS you can group products by groups, so there will be a specif group called : additional products) Step 5: Some of the custom product we have the option to automatically install WP based on the custom fields. So in step we should display the custom fields and labels ( if they are marked in WHMCS to be shown) and ask the user to fill. Step6 - The Billing/Contact info page. Two option: Already a client | New Client full description here: [login to view URL]