That's simply not correct.
It's an all stock transaction, so AppLovin can issue stock equal to $17.5B and transfer that to owners of Unity stock in return for their Unity stock. Then the two companies merge and the AppLovin stock owners now own both.
You can read details here:
> in a transaction where each outstanding share of Unity common stock would be exchanged for 1.152 shares of AppLovin Class A voting common stock and 0.314 shares of AppLovin Class C non-voting common stock. Under these terms, current Unity shareholders would receive approximately 55.0% of the outstanding shares of the combined company, with the Class A shares representing approximately 49.0% of the outstanding voting rights of the combined company.
https://www.businesswire.com/news/home/20220809005530/en/App...