Create complimentary tickets, and preview how they work before launching your page.
You'll want to go into your fundraising page's builder, afterwards, open up the sidebar and go into tickets.
Add your new ticket and leave the price as $0! Press save once you're done filling in the rest of the information.
That's pretty much it! You can see in the preview that the ticket reads as free. Update your page and you're good to start selling your tickets!