Paint bucket tool not working

Hi there, I'm trying to figure out how to colour in Animate with the bucket tool. I've tried many solutions, such as converting my drawings to symbols, duplicating the layer and colouring on the duplicated one, unlocking the bucket tool or even using different brushes (and making sure there are no gaps).

Even working on the line art layer won't work. I just can't seem to figure out why my bucket isn't even working! Can someone please inform me on what to do?