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. To complete Form I864, the petitioner must meet certain requirements.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. 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. There are several requirements to submit an I864 Affidavit of Support. The proof of U.S. domicile is one of those required documents. The joint sponsor must meet the same requirements as the original sponsor, the petitioner. The affidavit of support sponsor is required to meet certain income requirements, and be a Green Card holder or U.S. citizen.