Why when java 8 is installed Wakfu says it isn't?

I have a grandchild who wants to run a well-known interactive online game, Wakfu. It needs Java 8. We have installed Java 8 from the proper source (Oracle) and have done the latest security update. The Java control panel with the Apple System Preferences says it's installed correctly, but the wretched game says that it isn't correctly configured, and suggests we need to access a command line interface via another Java component.

Can anyone explain this? I am just about to dump Wakfu, but I thought I would see if there are any gamers who know what's up.

TIA