Android devices and browser works. IOS app gets a 55kb empty file. This happens with jpg, pdf and text files. IOS device can download file using browser without issue. The download does get the correct filename.
I uses the command
"system.perspective.download(filename=filename, data=filedata)"
I would report to support, I've come across bugs in the perspective app when downloading in the past. If it works on browser and android fine, it's likely a bug in the iOS version