Eraser and select tool not working on a drawing object within a selected layer.

I’m working in Toon Boom Harmony Premium and have been trying to erase a section of a drawing object I’ve been working on.

I select the eraser tool from the sidebar. I press my stylus against the trackpad to make the stroke. The computer signals that it has read my stroke by leaving a grey register trail in the wake of my cursor, but when I release my stylus and the grey trail disappears, the object stays the same.

I know for a fact that I am not on a different layer because when I turn off the visibility of the layer I’m working on, the object disappears. I also know for certain that I am using the right tool. Why is the tool not working, and what can I do to fix it?