Bitdefender BOX led blinking red means two things:
1. Bitdefender BOX cannot access the Internet and in this case you should contact your ISP.
2. Bitdefender BOX is in a DHCP conflict state which means that the DHCP functions are active on both Bitdefender BOX and router. In this scenario, you should also see a notification regarding this state in the Bitdefender BOX App.
You should connect to your router?s web interface, look for and disable the DHCP Server function, then reboot the router. In case you need help with this, please feel safe to contact Bitdefender BOX support and one of our skilled engineers will be more than happy to assist you.