I'm unable to get tracking information from their official website (
http://www.correos.es) which also seems to be extremely slow at the moment. So I think it's an issue on their side of things which I have no influence on.
If you are able to get tracking information from an official website (i.e. no third party tracking websites as I cannot use those), please let me know the link so I can see if I need to make changes to the app.
Sorry for the inconvenience!