I don't think you need the assets folder in your path.
Example: FileHandle handle = Gdx.files.internal("assets/coin/coins.scml");
Change to: FileHandle handle = Gdx.files.internal("coin/coins.scml");
I never point to "assets" because Gdx.files.internal already knows to look in the assets folder. With the code you have, it's like you are making it point to assets/assets/coin/coins.scml
Give that a try. Works for me. Also, on android it's possible you may need to edit the manifest file.