No, the Committee has NOT issued any formal letter of invitation, but only validated your application by simple mail during the last months (mail subjects: Confirmation for Assisi 2022 / The Economy of Francesco event 2022 – Reply): that is enough and you can proceed through official registration on the Participants Area.
In case you need the letter for VISA matters please ask for it by email to [email protected], or for other specific issues linked to work and study permission ask for it to [email protected].