In the Cognito dashboard, there is a list of standard attributes that we are given to choose from:

and in the docs, it says:
"You can only search for standard attributes. Custom attributes are not searchable. This is because only indexed attributes are searchable, and custom attributes cannot be indexed."
and when calling the API for ListUsers, filtering on "website", what I thought was a standard attribute, I get the following:
Cannot list users on the provided selector: website = "mywebsite.com"
Are these attributes not standard enough for this API call? or is my input just poorly formed?