I'm having this error in Joomla for some reason:
Call to undefined method Joomla\CMS\Application\AdministratorApplication::isSite()
I see other posts with this error, but I suppose they are using the Joomla app or installed on local files. In my class exercise, it is obligatory to use the web implementation of Joomla so I don't know how to apply the advice in other answers or if they even work.
Continuing with my case, I can't do anything. I can't enter the website, log out, see the administrator, edit my account, etc.
I am using Joomla 3.1.