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. In this guide, we will explain who needs to complete Form I864, when to file it, and how to fill out Form I864 stepbystep.The I864 Affidavit of Support is a signed document that a sponsor signs in order to accept full financial responsibility for the sponsored immigrant. This tip sheet will help you complete Form I864, Affidavit of Support Under Section 864A of the INA. Detailed Instructions for Affidavit. However, you must be at least 18 years of age and have a residence (domicile) in the U.S. before you can sign the Affidavit of Support (Form I-864 or I-864EZ). In today's video we're going to fill out form i-864 the affidavit of support form together. It is one of the most confusing forms. 1. Complete the entire Affidavit in black ink.