To have the best message receive experience on Xiaomi (MIUI 8), please do the following.
Step 1: Tap on the "Security" app.
Step 2: Tap on "Permissions"
Step 3: Again tap on "Permissions"
Step 4: Scroll down to find "hike" app and tap on it.
Step 5: Scroll down to the last option here which is "Display pop-up Window"
Step 6: Tap on this option and select "Accept"
Step 7: Once you see a "Green" check mark for this setting, notifications should work just fine for hike app.
If you still face any issues, please write to us at Support@hike.in and we will get back to you as soon as possible.