Here’s some information that also might help:

Follow this guide: https://xiaomifirmware.com/guides-and-tips/guide-unlock-xiaomi-redmi-note-4x/

And pay attention to this information: “You MUST flash 7.2.16 ROM, then go to the section How to Official Unlock Redmi Note 4X and Skip Step 2. Then follow the standard unlocking procedure using MiUnlock.”

Original post and credits goes to fmradio88: http://en.miui.com/thread-530781-3-1.html

Hi,

As far as we understood, for some reasons, guys from MIUI making the process of unlocking harder and harder each day. The “10008 api” error randomly appears on some devices, while other devices are unlocked without any problems. One possible solution could be is to turn off “OEM Unlock” option.

We’re currently looking for a working solution, and as soon as it will be found, we will post it here. While we’re trying to find a fix for the “10008 api” issue, here’s also a related topic on MIUI forum: http://en.miui.com/thread-548769-1-1.html

Please note that you’re doing everything at your own risk, and we’re not responsible for any damage done to your device.