Xiaomi does not have an official presence in many countries, including the USA. But that does not stop the importation of devices into countries that it does not officially support. If you import a device in any of these regions it will work without any problem as long as the bands of the providers are supported by the device. However, this is no longer the case.
More specifically, although Xiaomi’s export rules prohibit the sale of devices in Cuba, Iran, Syria, North Korea and Crimea, the company did not block the devices if someone introduced them. That is, it allowed activation. But now it does just that.
Numerous reports on Reddit and Facebook show that Xiaomi is blocking device activation and displaying the message: Xiaomi’s policy does not allow the sale of devices in the country where you tried to activate it, contact the country retailers for more information.