Terrain Texture Painting not working

I’ve created a terrain and made its texture a grass texture, and then added a good dirt texture to be painted on the terrain. I select the good dirt texture in the paint texture mode with the blue dot showing up, but when I click to paint nothing actually comes up-it doesn’t paint anything. I really have no idea what’s wrong. If anyone could help me I would really appreciate it.

What is the brush opacity set to? It should be around 0.8-1.