API integration of webpage for VoIP platform

Hello: We operate a VoIP platform. A particular customer base we work with does topup of international minutes for their customers. Our webportal for these customer is too comprehensive and I wish to create a very simple page whereby our retailer customer can insert a phone number, add money and click. Attached find image of existing page to create a new customer along with another page to add funds to an existing customer. We would like a page that looks more like the second image to add funds. The work would entail a - single page with a login. Login would be the retailer account and password. - The first field is to insert phone number o If it is a new account then the API would create new account with the entered phone number, insert a system created password, preselect default rate table. If existing account the add funds is all that is required o The second field is to insert funds amount o CLICK button The API index is available upon request. Please ask questions if your are not sure. thanks