Use this form to show they have adequate means of financial support and are not likely to rely on the US government for financial support. A) Complete an Affidavit of Support form and; b) Gather evidence of their finances and other supporting documents (See Step 5).The purpose of the Affidavit is to assist consular officers in determining whether a visa applicant will have adequate means of financial support in the US. In this guide, we will explain who needs to complete Form I864, when to file it, and how to fill out Form I864 stepbystep. In order to fill out an affidavit of support as a sponsor, you must be a U.S. citizen or green card holder. This tip sheet will help you complete Form I864, Affidavit of Support Under Section 864A of the INA. Detailed Instructions for Affidavit. 864 Affidavit of support How to fill out the Form 864 immigration Tips. The Affidavit of Support is a legal contract between the sponsor (you) and the U.S. government. It is important that the sponsor(s) carefully follow the instructions to determine which form needs to be completed, and how to complete the forms.