Campfire Pro is available on Steam. During seasonal sales (Summer, Winter, Black Friday), the software drops from $49.99 to as low as $14.99. Add it to your Steam wishlist, and wait for a notification. This is the safest way to get a legal key for under $20.
Without a license key, Campfire Pro usually runs in a restricted "Trial" or "Demo" mode. Activating the key unlocks: campfire pro license key
In the early 2010s, Campfire released public beta versions. Those keys were time-limited and have long since expired. If you find a key from 2016, it simply will not work on today’s operating systems. Campfire Pro is available on Steam