I drew wireframes to discuss with the product owner and developers to make sure the flow and functions meet the requirements. And make sure the flow can be carried out by the developers.
How to attract temporary users to download Picokey.
Where to put the Download Picokey button.
Floating button on default page
Users will see the download picokey button when they first come in, design A is on the top of the navigation bar, however after testing with my other coworkers, it will reduce the content space. After considering this problem, I redesigned it can be a floating button, users can close it if they don't need this function or can move to a better place not cover the page by themselves.
On setting up page
If users close the floating button on the default page, they can still find the button on setting page.
Pop up window to suggest to download the Picokey
When the user who didn't have Picokey on their device calls to other member, there will be a pop-up window to suggest them to download it. Or they can't use the Picokey to call to other members.