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. If you live outside the US but claim to be a US citizen, you will need to send in a written explanation and proof of your claim along with your Form I864. What documents must be submitted to National Visa Center? Upload the most recent version of Form I864 on USCIS website.