Use FluentResults for return failed validation with code 400

Please help me understand the best practice of using FluentResult in request validation. I developing a WebApi. I process error handling as described here: https://enterprisecraftsmanship.com/posts/rest-api-response-codes-400-vs-500/ Result.Fail generate internal server errors. Code 500. Great! This is what I need! But! I don't understand how to put bad validation in FluentResult to return 400 code. Result.Fail does not help me, because IsFailed generates InternalOperationexception 500. And I need to return 400(!!!) I want validation errors to not throw an exception, but output with a 400 code. What is the right way to do this in FluentResult?