Is Sandbox PayPal fake?

Could you please clarify for me? Is the Sandbox PayPal something that's actually legitimate, or is it a hoax? I've heard rumors about it, but I'm not entirely sure what the truth is. Could you possibly provide some insight into this matter? Is there any reliable evidence or documentation that supports the authenticity of Sandbox PayPal? Or, are there any red flags or concerns that I should be aware of? I'd greatly appreciate your assistance in helping me understand this better. Thank you in advance for your time and effort.