I can’t see in particular what’s wrong with your normal function, but I’d say it’s the culprit. Does it work when you connect the normals without the function?
Other very common reasons for landscape material not appearing are:
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Too much testing layers. Solution: right click on the any layer in the landscape paint dialog and choose ‘fill layer’, then try painting again.
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Run out of texture space. Solution: Select all the textures in your material and set Wrap in the details.