Taking screenshot of UI with Render Texutre

I am trying to build an image to share on facebook with a screenshot of game and some text. I can get the screenshot of the game with Render Texture. Than I put the image to a RawImage in a new canvas with the score and some text within a panel. When I try to take screenshot of this canvas it shows blank. Is there a way to take screen shot of canvas elements?

this is the manual.