It appears that the redirect for amazon prime shows is broken when selecting from a watchlist or discover.
I have tested on both Plex for windows and for android.
On windows, Plex opens a justwatch.com url which then redirects to an “amazon.au” address which does not resolve. Adding “.com.au” to the amazon address allows for a proper redirect.
Android reports “An error has occured, Please try again later” checking logging for the app it appears to also hit a justwatch address which when checked also redirects to amazon.au
All other services seem to redirect to the appropriate app, website or redirect to the app store.