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. The I864 Affidavit of Support is a signed document that a sponsor signs in order to accept full financial responsibility for the sponsored immigrant.The petitioner in question must fill out Form I-864 Affidavit of Support when petitioning and sponsoring an immigrant. This video will help you to fill out I-864 For Joint Sponsor. The petitioning sponsor must complete and submit a signed Form I864 for the intending immigrant even if a joint sponsor participates. If you have a joint sponsor, they must also complete Form I864. Cosponsors must also fill out an affidavit of support (Form I864) and meet the financial requirements independently. CitizenPath's software and Affidavit of Support sample can help you easily prepare a Form I864, Affidavit of Support, for your relative. You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. See tips for completing Form I-864.