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. Country of Domicile enter the joint sponsor's country of domicile (most sponsors will enter "US" as the country of their domicile). 6. To complete Form I864, the petitioner must meet certain requirements.