Use renderTexture with this.facebook.openShare

[BobBob]

Hi, I'm trying to user renderTexture to share what's on the screen.  Any help?  When I try it, it's not showing the image.  Here's a quick code snippet:
 

var rt = this.add.renderTexture(0, 0, 400, 800);
rt.draw('background',10,10);

rt.saveTexture('share_image');

var text = 'Whatever...';
var key = 'share_image';

this.input.on('pointerdown', function () {
          this.facebook.openShare(text, key, 0, null)
      }, this);

It works if I just share an image directly, like this:

var text = 'Whatever...';
var key = 'background';

this.input.on('pointerdown', function () {
          this.facebook.openShare(text, key, 0, null)
      }, this);

I'm really stuck on this.  It seams like it should work to share via renderTexture.  Am I missing something?  Any help is greatly appreciated.  Thanks everyone!!!