"Thank you for the invitation."
That's a term that fell out of usage, modern dictionaries usually don't even list it; the Crusca already in 1923 ( http://www.lessicografia.it/pagina.jsp?ediz=5&vol=8&pag=1201&tipo=3 ) wrote "non è voce di uso comune" (it's not a word commonly used).
Oh thanks. It wasn't clear because I translated it by myself based on my Italian experiences. I found that English words of Latin origin, ending with 'tion', like 'invitation', can be translated to 'zione', hence 'invitazione'. But as it appears, it doesn't work always. :(