Invitation letters are not necessary for issuing visitor visas. You can write your own invitation letter, which may specify:Comprehensive guide to writing an invitation letter for your US visa application, with free samples and tips. What should the letter say? The letter should include specific details like your relationship with the visitor, the purpose of their visit, duration of stay, and financial arrangements. The template is designed in both A4 and US letter sizes, accommodating international and domestic visa requirements.