In case you missed it, back in January The Pokémon Company confirmed it would be discontinuing its Pokémon TV service on 28th March 2024.
As we've now passed this date, the app and browser will no longer function across multiple devices including the Nintendo Switch, iOS, Android and Smart TVs. When you boot up the app on Switch, you should receive the following Error Code:
Error Code: 2124-4609 - "This online service has ended. Thank you for your interest"
Serebii.net mentions how some people are still apparently able to access the app, but this likely won't be possible for much longer.
This app and browser, which was made available on the Switch eShop in 2021, allowed fans to watch past episodes of the Pokémon anime for free. If you want to keep watching the Pokémon anime, you can still catch it on platforms like YouTube, Netflix, Prime Video and various other services. Check out the official website for more details.