After upgrading/downgrading, the box shows a red light, and the phone cannot connect to the box.

Solution:

1. Reset the car infotainment.

2. Delete the Bluetooth pairing record of the box from the phone.

3. Access product backend 192.168.50.2 to reset the box in the settings. You may refer to the blog below to access 192.168.50. (Upon the first visit to this webpage, you may need to provide car model information and submit it.) 

https://carlinkitcarplay.com/blogs/carlinkit-4-0-cp2a-faq/how-to-visit-website-backstage-192-168-50-2