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. If you have a joint sponsor, they must also complete Form I864.In today's video we are going to be filling out form i 864 the affidavit of support form for the joint sponsor. The I864 Affidavit of Support is a signed document that a sponsor signs in order to accept full financial responsibility for the sponsored immigrant. You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. See tips for completing Form I-864. This tip sheet will help you complete Form I864, Affidavit of Support Under Section 864A of the INA. Detailed Instructions for Affidavit. The petitioning sponsor must complete and submit a signed Form I864 for the intending immigrant even if a joint sponsor participates. This video will help you to fill out I-864 For Joint Sponsor.