How to open up an extension point to a third-party app (extension)

According to the documentation, using Scope(restriction: .none) can expose the extension point to third-party app extensions. Below is my implementation, which ultimately results in an error.

Code for declaring the extension point:

@available(iOS 26.0, *)
extension AppExtensionPoint {
    @Definition
    static var priceExtension: AppExtensionPoint {
        Name("priceExtension")
        UserInterface(false)
        Scope(restriction: .none)
    }
}

Code for locating the extension point:

monitor = try await AppExtensionPoint.Monitor(appExtensionPoint: .priceExtension)

When executing the code to locate the extension point, the following error occurs: However, in practice, I found that declaring the extension point in this way results in an error when trying to locate it:

Error Domain=com.apple.extensionKit.errorDomain Code=19 "Failed to add observer" UserInfo={NSLocalizedDescription=Failed to add observer}