If you are ready to pay with us at the time of ‘Free Registration’ (or) ‘Free download’ Itself, whether you get or not any payment from the users in future. There are Free projects.
Examples for pay per free registration:
A) You are flat developer or Banking product marketer like Loans, Insurance, Investment. You want to develop a potential database to follow them. So, you want lead by free from interested persons whether you will get or not any payment from the users in future. B) If you start your X (or) Y (or) Z companies. Financial valuation of your site is depending upon number of users. So, you have to promote. To promote that, you pay us for every free registration whether you will get or not any payment from users in future.
Examples for pay per free download:
A) In very near future all businesses will be with mobile application. Every mobile app-based business is worthfully when it has more and more users than competitors. So, every mobile application requires download promotion campaign. When we promote this app, developer pay us for every free download whether he will get or not any payment from the user in future. B) A Software developer want to spread. So, they release their first free version for market penetration. Then, he will pay us for every free download whether he will get or not any payment in future.

If you ready to pay us, whenever user will pay you whether you give or not give free package/ free trail period to user at the time of joining is pricing project.
Examples:

1. Pay per sales: You are selling anyone product or service or membership or book with or with out free trial or free package. When a purchaser pays to buy your product in our promotion you pay us.
2. Pay per recurrence: You are running regular subscription-based service. When a regular subscriber joins with you in our promotion, you pay us whenever the subscriber pays you.
3. Pay per transaction: You project is even though not as regular and even priced as subscription-based business, but frequent and irregular value transaction, you pay us whenever transaction will happen by the user who introduced by us.

Legality, online trackable, genuine pricing, Quality, refund feature, Promotional remuneration are the factors to accept new one. Any low or negative rating or review or compliant from Government or user or promoter are the factors to delete the existing one.

This is not just advertisement project like ‘Pay Per Banner view’or ‘Pay Per Click’. This is result oriented promotional project. Target user identification, educating them, clarifying them, influence them, follow up them, promotion finalization with final performance. All are executing with human interactivity which is a must one for any promotional activity.