The setup you’re describing should just work. Access to external APIs is supported, except for a few specific APIs that are blocked. Those include the Telegram API, but it looks like you’ve found a workaround for this.
However, it looks like there is something going on with the DNS resolvers that’s blocked some domain names, including *.workers.dev, from being accessed.
I’m looking into this to see if I can find out what’s going on here.
Since there are multiple topics about the same issues with workers.dev, let’s move the discussion to the oldest one here: