Charts: How to show string on only on series point hover

Hi,

I have a simple chart with Y axis as Cost and X axis as Year. I would like to insert a string in the hover info bubble, but without that string showing up in either X or Y labels.

This is what i am needing to create in Visualizer (a mockup image):
https://snipboard.io/o4gcCa.jpg

This is what i have so far, in Visualizer:
https://snipboard.io/WnKHDe.jpg

So, i am needing to add “Basic”, “Intermediate”, and “Advanced” in certain points. Any advice would be helpful! If i need to get pro, i can do that.

Thanks!
Ben

The page I need help with: [log in to see the link]