Q: What’s F-code of Xiaomi Phone?
A: The full name of F-code is Friends Code. It’s born to provide priority with important users who’ve greatly contributed to Xiaomi at first. They can directly buy Xiaomi Phones or other items from Official web without ordering in advance. It can only help buy, cant be used or exchanged as money!
I’ve never seen one generally given out in the clear on Weibo before.
Mike Cane’s xBlog 
My mi4 smart flip case white is changed
My f code
please tell a F-Code
Used in limited-quantity flash sales of the past.