input – Button with hexagon shape not recognizing mouse click

I made a hexagonal button, with a png image, the problem is that if i click outside of the image of the hexagon(but still inside of the squared area that defines the whole button), the click is registered , if i click inside of the button nothing happens, now i just read in the docs about the property Click Mask, so i made the same image of the hexagon shape into a bitmap, but this error text comes up:

The selected resource (StreamTexture) does not match any type expected for this property (BitMap).

I used this linkt as a guide to create the bitmap, http://www.herongyang.com/Windows/GIMP-JPEG-Save-Image-in-BMP-Format.html, still i don’t know what i’m missing.
Also used MS Paint to save it as bitmap, but that din’t work either.

Why i can’t load the image as Click Mask in Godot?

I attached the image for testing.

enter image description here