Dear,
I went through your requirement and I understand your project (add ons in the php script) . once we take down your complete requirement we will provide the solution document for your project .If things fit in your school of thought, we can kick start the work within your budget. Please open the chat to proceed further.
MY UNDERSTANDINGS:
1. fills in Invoice, Amount & Description in form for customer
2. Invoice, to payment information
3. Company Name & Phone Number input to billing data
4. Adding checkbox: “Ship to billing address” in “Billing Information” that will auto fill shipping data.
5. “Shipping Information”,
6. CHECK "I agree to terms…" box, that needs to be check before clicking submit.
7. Make a simple page they will generate the url for: name, Company, invoice, amount, description, email, phone
Thanks