Hi Carter,
Use this module for Native file download:
A java script action is present to download file in native.
https://marketplace.mendix.com/link/component/114252
Also, you can refer to this forum post. This post will give you an idea of why your usual Download file activity does not work in native apps.
https://forum.mendix.com/link/space/mobile/questions/110086
Dinesh, here is a picture of my updated nanoflow: