I want to create a chart of the time a user is spending on Moodle using the Charts API. After a few failed attempts, I decided to try the simplest example I could think off and I copy-pasted the 'Mixed chart types' example of the documentation (php 'test' attached). It still didn't work (picture 'test' attached). I then decided to try if some examples of the Charts API in the core of Moodle worked. I tried with both the quiz/report/overview (picture quizreportoverview attached) and the blocks/ranking/graphs (picture blocksrankinggraphs attached). It still didn't work.
So I have 2 questions :
1) Are my use cases correct or am I making a mistake somewhere.
2) Am I missing something in the configuration of my Moodle ? The admin/environment.php tells me that everything is fine.
I am on Moodle 3.4 with php7.
Thanks in advance.