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.This video will help you to fill out I-864 For Joint Sponsor. If you have a joint sponsor, the joint sponsor must also complete and sign USCIS Form I-864. The I-864 Form assures that the petitioning family member is willing to support the person wanting lawful resident status financially. You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. See tips for completing Form I-864. Form I-864: Affidavit of Support. An Affidavit of Support is US Immigration Form I-864. 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.