This audio guide app by the company Artymax is heavily advertised at the entrance the the Royal Alcazar. You can scan the QR code and download their (unofficial but they're the only vender) app for a fee.
The app is really problematic, however. It doesn't work with bluetooth earbuds. So you would have to hold your phone up to your ear while simultaneously trying to look at their content, while also trying not to annoy the other visitors who are also listening to the app. And you cannot really navigate the app easily. You have to restart each section from the beginning if you stop it.
It just completely sucks. There's a reason it has almost entirely 1-Star ratings