error in ResourceDictionary using xamarin

Hi, I'm trying to use the x: key of this class

<Application xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:infra="clr-namespace:Lands.Infrastructure"
         x:Class="Lands.App">
<Application.Resources>

    <!-- Application resource dictionary -->
    <ResourceDictionary>
        <infra:InstanceLocator x:Key="Locator" />
    </ResourceDictionary>

 </Application.Resources>

when trying to run the program, I get the following error

reviewing and I do not know if it is the problem but in the method already mentioned the Key function does not exist. (I think so)

some idea of the error thanks