The side key flex cable includes internal buttons for the power and volume controls.
This is a replacement for Xiaomi Mi 4i, When you turn up or turn down volume button, and the volume still the same as before, or you press power button, it is not any reaction, which mean side button flex cable has something wrong, you need the item to replace.
Parts offer a 90-Day warranty. The warranty period covers any defects in the material or the workmanship of the product. Warranty does not cover any damage done while using the product. Any product returned within warranty period will be eligible for a refund or a replacement.