Dow do I use WeatherKit Swift framework to fetch the weather inside a Widget Extension?

I can't fetch the weather using the WeatherKit framework inside a Widget Extension.

Here's a project I created just for this example. This widget shows the humidity of a sample location.

Here's the code:

import WidgetKit
import SwiftUI
import WeatherKit
import CoreLocation

struct Provider: TimelineProvider {
    func placeholder(in context: Context) -> SimpleEntry {
        SimpleEntry(date: Date(), humidity: 9.99) // placeholder humidity
    }

    func getSnapshot(in context: Context, completion: @escaping (SimpleEntry) -> ()) {
        let entry = SimpleEntry(date: Date(), humidity: 9.99) // placeholder humidity
        completion(entry)
    }

    func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> ()) {
        Task {
            let nextUpdate = Date().addingTimeInterval(3600) // 1 hour in seconds
            
            let sampleLocation = CLLocation(latitude: 51.5072, longitude: 0.1276) // sample location (London)
            let weather = try await WeatherService.shared.weather(for: sampleLocation)
            let entry = SimpleEntry(date: .now, humidity: weather.currentWeather.humidity)
            
            let timeline = Timeline(entries: [entry], policy: .after(nextUpdate))
            completion(timeline)
        }
    }
}

struct SimpleEntry: TimelineEntry {
    let date: Date
    let humidity: Double
}

struct WidgetWeatherTestWidgetEntryView : View {
    var entry: Provider.Entry

    var body: some View {
        Text("\(entry.humidity)")
    }
}

struct WidgetWeatherTestWidget: Widget {
    let kind: String = "WidgetWeatherTest"

    var body: some WidgetConfiguration {
        StaticConfiguration(kind: kind, provider: Provider()) { entry in
            WidgetWeatherTestWidgetEntryView(entry: entry)
        }
        .configurationDisplayName("Widget Weather Test")
        .description("Testing weatherkit in a Widget")
        .supportedFamilies([.systemMedium])
    }
}

It works fine in the simulator:

But it doesn't work in a real device. As soon as I call WeatherService's weather(for: CLLocation) async throws -> Weather the widget get's "blocked":

I've tried moving the try await WeatherService.shared.weather(for: sampleLocation) to different places, but nothing worked. As soon as I comment out this line (and create an entry with a placeholder humidity) everything works.

I added the WeatherKit capability in the main app target and in the WidgetExtension target. I also added the WeatherKit "Capability" and "App Service" in the "Certificates, Identifiers & Profiles" of the Apple Developer website.

The WeatherKit framework works fine in other parts of the main app.

I haven't tried using the WeatherKit REST API, yet.

Any ideas what could be happening?