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 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).Completing and signing Form I-864 makes you the sponsor. Please submit proof of domicile. To complete Form I864, the petitioner must meet certain requirements. You need to submit more evidence of the petitioner's US domicile or intent to establish US domicile.