FluentValidation: Client-side validation not working

I have a validator that is working correctly but I haven’t yet been able to get the respective client-side validation to work.

    FluentValidationModelValidatorProvider.Configure(provider => 
            {
                provider.ValidatorFactory = new BrandValidationFactory();
                provider.Add(
                            typeof(RequiredIfStatusIsEmployedOrSelfEmployedValidator),
                            (metadata, context, rule, validator) => new RequiredIfStatusIsEmployedOrSelfEmployedClientValidator(metadata, context, rule, validator));
            });

RequiredIfStatusIsEmployedOrSelfEmployedValidator inherits PropertyValidator and overrides the protected method:

protected override bool IsValid(PropertyValidatorContext context)
        {
            if (!EmployedStatuses.Contains(applicationFormContext.Application.MainApplicant.EmploymentStatusId.ToUnderlyingType().ToString(CultureInfo.InvariantCulture)))
            {
                return true;
            }

            return context.PropertyValue != null && !IsInvalidString(context.PropertyValue);
        }

RequiredIfStatusIsEmployedOrSelfEmployedClientValidator inherits FluentValidationPropertyValidator and overrides the public method:

public override IEnumerable<ModelClientValidationRule> GetClientValidationRules()
        {
            yield return new ModelClientValidationMinLengthRule("testError1", 100);
        }

Finally, the configure method:

FluentValidationModelValidatorProvider.Configure(provider => 
            {
                provider.ValidatorFactory = new BrandValidationFactory();
                provider.Add(
                            typeof(RequiredIfStatusIsEmployedOrSelfEmployedValidator),
                            (metadata, context, rule, validator) => new RequiredIfStatusIsEmployedOrSelfEmployedClientValidator(metadata, context, rule, validator));
            });

The client validator never gets called and, therefore, the data- attributes never get rendered on the HTML.

What am I missing?