Fluent validator: How to validate a string to be not empty when another field is specific value from enum

Question

I need to add validation for Message only when Type is Other

I tried to use Must, and validation works when type is Other, but when type is First I receive "The specified condition was not met for 'message'.",

 enum Types
 {
     First, Second, Other
 }

 class MyRequest
 {
    public string Message { get; set; }
   
    public Types Type { get; set; }
 }

 public MyRequestValidator()
 {
     RuleFor(x => x.Type)
         .IsInEnum();
     RuleFor(x => x.Message)
         .Must((model, field) =>
         {
             if (model.Type == Types.Other)
             {
                 return true;
             }

             return false;
         })
         .NotEmpty()
         .WithMessage("Message is required when type is Other")
         .MaximumLength(10);
 }

Any ideas how to validate a string when another prop is a specific value from an enum?

Answer 1

looks like When proposed by SaeedEsmaeelinejad soled my issue

 When(x => x.Type == Types.Other, () => {
                RuleFor(x => x.Message)
                    .NotEmpty()
                    .WithMessage("Message is required when type is Other")
                    .MaximumLength(10);
            });