Script to copy and paste layers between sprites

Hi, Using a script I am trying to copy layers from one open sprite (.ase) to another open sprite. I have the basics working but I am failing to copy over the layer.
I loop over the layers of my source sprite and try the following -
app.activeSprite = sourceSprite
app.activeLayer = sourceCurrentLayer
copy = app.command.copy(sourceCurrentLayer) – ? Do I pass in the layer or rely on active?
app.activeSprite = destinationSprite

As it runs through in Aseprite it correctly selects the layers but does not appear to perform the copy?

Anything obvious I’m missing? I’m new to Aseprite so could be something obvious.