"Don't worry. What are you afraid of?" is not accepted.
“Please relax” should be 请放松
Also 请放心 is more idiomatic than 请放松.
请放心 is Please relax, calm down, chill. Don't worry is 别担心
請放心 is more akin to "do not worry."
"Please relax. What is it that scares you?" Should be accepted. Reported.
Please relax. What are you so afraid of?
Please relax, what do you fear?不行吗
Please rest assured should be correct
That sounds a bit creepy)