Fluent validation: When method not found after Equals

Blazor sever-side, .NET7, using Nuget package Blazored.FluentValidation version 2.1.0

I have a model that includes two bool properties IsAdmin and Agreed. The first is for internal use (to skip certain checks when the logged-in user is an admin) and the second is to say the user has accepted the terms and conditions before submitting the form.

I want a validation rule that checks that Agreed is true when IsAdmin is false. I tried the following...

RuleFor(p => p.Agreed)  .Equals(true)  .When(p => !p.Admin)  .WithMessage("You must accept the terms and conditions");

...but got a compiler error on When...

Cannot resolve symbol When

I'm not sure what I've done wrong, as I've used When in other places without problem, eg...

RuleFor(p => p.SelectedTimePackageId)  .GreaterThan(0)  .When(p => p.SelectedPrintPackageId == 0)  .WithMessage("You must select a time package and/or a print package");

I know I can get around this with a custom validation rule, but would like to know why When isn't resolved.