Cannot paint Texture onto Terrain using Custom Material 2018.4

Hi so I am currently using Unity 2018.4.0f1. I created a terrain. Went to Terrain Settings > Basic Terrain > Material > Custom and then added a Custom Material (Attached to the material is just the Standard Shader). Problem now is that the Terrain won't let me paint any texture to it. However, on Unity version 2017.4.1f1, doing this exact same thing as mentioned above, it actually works. Is this something that Unity got rid of going into 2018? Or am I doing something wrong?