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).Providing proof of domicile in the United States is critical for most people when submitting Form I864, Affidavit of Support. To complete Form I864, the petitioner must meet certain requirements. Proof of U.S. domicile is required for the I864. Learn examples of proof of domicile along with proof of domicile documents required.