Paid-in, also known as paid-up capital, is the money that a company raises by selling shares of its stock on the primary market directly to investors, usually via an IPO (Initial Public Offering). The goal here is to transition from a private to a public company. 

If a listed company wants to raise more money after its IPO, it can issue additional shares on the primary market. This is called FPO (Follow on Public Offer). 

When investors trade shares of a company, they do so on the secondary market. In this case, the company doesn’t receive any additional paid-up capital because the proceeds of those transactions go to the shareholders selling their purchased stocks.

Paid-up capital is a part of authorized capital. Authorized capital is the maximum amount of capital that a company can issue shares for. Paid-up capital is the money that a company ends up receiving after the issue of shares.