Dear Moonvalk,
I'm sorry that you had isseus while trying to add the GDScript version of the plugin. It should work just fine in the .NET version of 4.7, as with the normal version. From your error messages I can see that you might have set incorrect names for the plugin folder. I think you named it "AssetPlacer", although it needs to be named "assetplacer" in lowercase letters. Please try to rename the folder and restart Godot to see if it fixed the issue.
Best regards and happy developing