Like sfdex said, You do have to set the "let light through" options in the Raytracing box.  I don't think you have to in the GI box.   BUT the trick seems to be in the texture.   The Transparency option must be on and then the shader has to be set to something other than none.

In the attached example, (render is overlayed teh texture options) I set the Color Map to a texture, the transparency to the same texture and the transparency's shader to the same texture.

hope that helps, I'm a stranger here myself.

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Phillip Drawbridge
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