DataBinding Error No Property, Bindable Property or Event Found

Hey Guys,

i want to make a Bindable Property but i get this Error:
No Property, Bindable Property or Event Found

in Xaml:
Checked="{Binding NoticeUserData}"

in my class:
public static BindableProperty CheckboxProperty =
BindableProperty.Create(nameof(Checked), typeof(bool), typeof(Checkbox), true);

public bool Checked
{
get
{
return (bool)GetValue(CheckboxProperty);
}
set
{
SetValue(CheckboxProperty, value);
}
}

What do i miss? Can anyone help me i have never done before a databinding Property.

Thanks for help!