What you have is correct but I suspect based on your error messages you did not add the properties namespace in your xaml.
At the top of the xaml document you will see things like this:
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
These are xaml namespaces, similar to using statements in C#. You need to add your properties namespace to this section like this:
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:properties="clr-namespace:{yourproject}.Properties"
just replace {yourproject} with whatever your projects namespace is.
You can find a working example of what this looks like here:
https://github.com/AlexLexicon/Discord.Example.BindingSettings