I guess this is a bug (I can not find where to change this myself), as you can see in the image, both on the title and on the button it shows “Registrarse” which means Sign up in spanish, where this should be Log in (in spanish “Iniciar sesión”) right?
You should be able to change that by activating the multilanguage feature in your TagoRUN. Then you can go to the dictionary (make sure you generated a new one from the TagoRUN screen) and change the text in the spanish language.
If you don’t have a Scale plan, make sure you set spanish as the fallback language.