Comprehensive guide to writing an invitation letter for your US visa application, with free samples and tips. There is no requirement for an invitation letter.If you want to send on send it to your parents who in turn may present it to the US consulate. Describe the visit in detail. Include the invitee's full name, passport number, and date of birth. The letter should include specific details like your relationship with the visitor, the purpose of their visit, duration of stay, and financial arrangements. Official Invitation Letter. Download the Official OTC Electronic Invitation Letter. What should the letter say? Document Requirements.