Providing proof of domicile in the United States is critical for most people when submitting Form I864, Affidavit of Support. 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). The I864 Affidavit of Support is a signed document that a sponsor signs in order to accept full financial responsibility for the sponsored immigrant. Joint sponsors don't need to prove domicile. The petitioner needs to prove domicile or the intent therof. You must live in the United States or a U.S. territory and have proof of domicile. Must meet the financial requirements. The petitioning sponsor must complete and submit a signed Form I864 for the intending immigrant even if a joint sponsor participates.