If you have a .edu email address, you can apply for a one-year free license.
Chaos offers a fully functional, watermark-free 30-day trial of V-Ray for Cinema 4D.
V-Ray is commercial software (~$80/month or $470/year). Chaos Group is a private company that invests millions in R&D. However, they do offer legitimate ways to use V-Ray for free.
The term "free download" is the most searched phrase in the 3D community, but it comes with caveats.
The Official Route: Chaos Group does not offer a fully functional, permanent free version of V-Ray. However, they offer the next best thing for professionals: a 30-Day Free Trial. This is the "ultimate free download" because it gives you unrestricted access to the full software. It allows you to stress-test your hardware and see if the workflow fits your pipeline before committing to a subscription or perpetual license.
The Educational Route: For students and educators, Chaos Group is incredibly generous. They offer free educational licenses for V-Ray for Cinema 4D. If you have a valid .edu email address or proof of academic enrollment, you can download a fully functional version of the engine for the duration of your studies. This is the legitimate way to master the engine without cost.
When you are using your free trial, time is limited. Don't waste days on these errors: