I can't fill a shape

There are many possibilities.

Check whether the graphic is on the same layer.

Check if line have a combination(Preferably after the full selection Ctrl + B)

Talk about my process here.

1,Draw sketches with brushes and erasers.

2,Create a new layer, draw a complete outline with a brush or pencil.

3,Create a new layer use a pen or pencil to paint the picture again,and draw tween.

4,Clear an extra line or error.

5,create a new layer,Adds a tween to the drawing,

6,create a new layer,Fill Color(The color is below the contour layer)

7.create a new layer,Copy the outline to the top of the color, below the outline,Where shadows and highlights are drawn

8.and then output

Cannot automatically check for closure, so you can use a line or brush to select.

pencil

Brush

You do technically have a "gap" in your image at the very bottom where your character's body starts. Animate will not fill in the shape if there's any gaps.

Additionally, it looks like you're using the Brush tool to draw your character. I would suggest using the Line or Pen tool instead. This will give you more flexibility and allow you to section off areas of your drawing.

Assuming that you used the Line tool, if you wanted to just fill in the ear, you can draw a line across the ear in order to section off that area. You should then be able to fill the ear where you sectioned it off. After you're done, you can then select and delete the line that you used to isolate the section of the ear.