We are building a web application where a company can buy a license which costs $300 and extra users which cost $10 for one year. Suppose company bought a license and 10 users. They will pay $300+$100 = $400.
After some months if the company wants to buy extra users, they can buy those but they will have to pay remaining days cost at the prorated basis. Like if they buy 1 extra user after 6 months, they will have to pay $5.
So after the license is expired, we want that to be auto-renewed with license cost and users cost for next year which will be $400+$10 = $410. Is there any API for such renewal process?
Also, we are using Paypal API based approach in the application and hence for payment, we need not go to Paypal's gateway. Can I know the maximum limit for such transaction? Is it $10,000?
By default PayPal's limit is $10k but you can call and request they raise that limit.
For what you've outlined it would be best to use Reference Transactions. This way you won't have any limitations on when you process a payment or what amount to process.
For regular PayPal payments you'll need to setup a billing agreement and use the billing agreement ID in future reference transaction requests. For direct credit card you don't need a billing agreement.