An unknown error has occurred.是发生了未知错误的意思，例如
As many people want to access the website to book for an vaccine appointment， website can't copy， then there message will be seen :an unknown error has occurred. 由于很多人想访问网站进行疫苗预约，网站无法复制，然后会看到消息：发生未知错误。
An unknown error has occurred.是发生了未知错误的意思，例如
As many people want to access the website to book for an vaccine appointment， website can't copy， then there message will be seen :an unknown error has occurred. 由于很多人想访问网站进行疫苗预约，网站无法复制，然后会看到消息：发生未知错误。
