I managed to get it to work a few months ago by importing the toon line pack from unity standard assets and attatching the edge detection to my main camera but now I get errors when I try import image effects. so I tried importing the free cartoon shaders pack and changed the main shader in graphics settings to deferred and put it as the toon outline shader and changed my camera shader to deferred but that just made my scene entirely black.
Are we talking about outlines or cell shading here? As for cell shading it might be interesting what style you want o achieve. I think a good option would be to use the cell shading only for lights (and shadows). This you can achieve with a custom light pass, take a look at toon ramp in the examples: Unity - Manual: Surface Shader lighting examples (If you don’t use a gradient, but more like areas, you will get cell shading).
As for outlines, I don’t know anything about the asset you are mentioning, but there is a good open source project out there that might fit your needs: GitHub - cakeslice/Outline-Effect: Outline Image Effect for Unity
The vast majority of toon / cell shaders are for forward rendering only. If they already have support for an outline built in (like those that come with standard assets) they may end up rendering a solid color like you saw (edit: when rendering using deferred).
If you want to do deferred cell shading, you may actually be able use the built in Standard Shader, but you have to replace the deferred shader.