Is it really possible to jump into an active volcano?

In some cases. Most volcanoes aren't hawaii-type volcanoes with a semi-permanent lava pool, and even when there is a pool, the pool does not always fill a large basin with steep sides so you could walk up to the edge and jump like at an abandoned quarry filled with water. It is possible and does happen that you can get right up to the edge of that pit before you get hit by the heat emanating from below, but it isn't "normal". Even without the heat, there are noxious gases or fumes that make it pretty unpleasant even when not potentially deadly.

So yes, you could, but no, you usually would not be able to.

Yes, it is possible to jump into an active volcano, if the crater is open enough to fit you inside. The volcano does not have to be actively ejecting gas or material at that moment, and the heat is not always going to affect you at the mouth of the crater. But once you make the jump, you will, at best, break both of your legs in the fall, and at worst, die very painfully.

You'd get a hot bum!!!!'

Empedocles did.

Great Empedocles, that ardent soul, Leapt into Etna, and was roasted whole.

Yes. Check out the link below. Sleeping inside an active volcano.

The short answer is yes, but not in every case. Some volcanoes, like Kilauea in Hawaii, have an open caldera, which means that the top is open and anything can fall into it. Others have a much narrower 'throat' (so to speak), and may be sealed until an actual eruption is taking place.

I have walked across the Crater of an Active Volcano. Did not have to Jump, just walked down the Trail. Walked up to the Center of the Crater and looked down into the Lava Pit. The Lava Pit has a name: Halemaʻumaʻu The volcano is Kīlauea. One of the most active volcano's in the world.

It's possible to jump into a live volcano but not likely to survive and tell the tale.

Yes but only once

Yes it's possible. If the lava pit is deep enough the heat would be barrable enough to walk up to. You can watch videos on youtube of scientists throwing stuff into active volcanoes. They wear those silvery suits but those suits don't deflect all the heat waves so they are still burning in those suits.