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).If both beneficiary and sponsor are living abroad, you'll need to supply evidence of U.S. domicile with your Form I-864. One of the requirements for Form I864 is showing that you are domiciled in the US. In other words, your principal residence must be located in the US. Line-by-line guidance for properly filling out USCIS's I-864 Affidavit of Support to sponsor an immigrating family member. Providing proof of domicile in the United States is critical for most people when submitting Form I864, Affidavit of Support.