Amby Transfer Problem

I’ve bought the two available sound packs for Model Cycles, plus the free one.
The Transfer app has managed to transfer two of the packs, but refuses to move the Amby pack.
I’ve downloaded it again, made sure I’m on latest version of Transfer, and I still can’t send it to device.
Is this familiar to anyone?

You may have done this already, but unzip the downloaded file and copy it to your desktop. Transfer will not let you transfer the original download file, it has to be copied for some reason before you move it into the app

Unzipped it, but not tried copying it. Thanks, I’ll give it a try.