UMG Widget Texture to Post Process Material

Hi all,

I want to use a UMG Widget as a texture in a post process material and I cannot find a solution as to how to do this.
I read elsewhere that you can get the render target of a widget component. I have tried using this to set a texture parameter in a material but it seems to be invalid somehow as the material uses the default engine texture instead.

As you can see in the image below, the tiled cement texture is what happens when I assign the widget render target, seems to be invalid somehow…

Please let me know if anything is unclear.
Thank you!