The ISSO provides a sample invitation letter template as a courtesy but cannot guarantee that your visitor will have their visa approved. You should include the name of the host, formal expression, the event purpose, date, time, and venue, contact details, and RSVP.This post contains a guide to writing your own Invitation Letter for Immigration and a sample Affidavit of Support and Guarantee for visiting relatives abroad. For your convenience, please find below a free sample letter of invitation you can modify to suit your particular situation. Use an appropriate tone. Explore a collection of formal invitation letter samples for various occasions. What Should I Write in a Letter? âť’ Information About Yourself. Check out this sample letter for an event invitation. It's perfect for business events and can be customized to fit your needs.