These additional financial sponsors also have to submit an Affidavit of Support, proof of their income, and proof of their legal status in the United States. If you have a joint sponsor, the joint sponsor must also complete and sign USCIS Form I-864.If you want to sponsor someone for a family-based green card, you need to provide proof of a U.S. domicile in your Affidavit of Support (Form I-864). On Form I864, petitioners must prove that they have the ability to financially support the visa applicant(s) if necessary. In this video we're going to show you how to complete an i 864 and affidavit of support that is needed as part of the package for an adjustment of status. What Documentation and Evidence Are Required of a Sponsor? The I-864 is an Affidavit of Support.