Which government department issues the so called red letter or visa notice

I am a first time traveller to china and I applied for my entry permit with the official invitation letter from the exhibition organizer but the local embassy here in Colombo said I need the official government letter from the so called relevant government department but the embassy doesn't mention from which government department my inviter need today get this letter as I am a fist time visitor . And my sponsor the show organizer is having a hard time figuring out where he can get this so called red letter or government letter also known as a visa notice from . Please advise from where my inviter needs to obtain this letter from to be sent to me .. Thanks