A lead, in this business, is a person who has handed over contact details and shown some sign they might sell or buy. A lead generation platform, used strictly, means a product other people pay to use or pay to receive output from, so a subscription dashboard, a marketplace that takes a cut of each transaction, or a data tool with logins. Used loosely, people call a landing page plus an ad account a platform too. That second thing is a funnel you own. It can make good money. It stops making money the day you stop buying ads, and there's nothing there for someone else to pay a monthly fee for.
The funnel is cheap to stand up. A domain and hosting are under $200 a year, a CRM that can hold and route leads starts around $100 a month, and then ad spend is whatever your market charges. Seller keywords on search can run $30 to $60 a click in a busy metro, which is why people go to direct mail or social instead.
The part that catches people is the other side. Leads are only worth something if you have buyers waiting who will pay reliably and keep paying. Most people build supply first and then discover their three buyers all stop answering in a slow month.
One more thing to sort out early: getting paid for connecting a seller to a buyer can touch real estate licensing rules, and those are set state by state, so ask a local attorney what your specific arrangement counts as before you take money for it.