Erasing a texture is a bit weird with Blender at first. You need to be erasing a slot that’s NOT the base slot. Because you can’t erase a texture that has nothing underneath it.
So if you’re painting the diffuse color layers, make sure you have 2 diffuse color slots, and on the second, change your brush’s Blend mode to Erase Alpha. That should enable you to erase. But keep in mind you need to have something to erase. If your second texture slot is 100% alpha (set to black) you’ll have nothing to erase.
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