I’m not sure what Discord library you’re using, but I would imagine that .setImage is expecting an image, not their Twitch channel page URL. If you want to manually specify an image of their stream then you should use the Get Streams endpoint and use the provided thumbnail.
Also to note, creating streaming announcements based on presence changes on Discord is not a reliable way to know if a channel is live or not, as it’s possible to show as ‘streaming’ on Discord even when the channel isn’t live.