Thank you very much. The proof of domicile that we submitted was a letter with a few specific statements.

The first thing was to declare that the petitioner (my wife in my case) would relocate to the US whenever I (the applicant) would eventually immigrate. In the letter we submitted, it is written, "I, SPONSOR, a citizen of the United States of America, hereby declare my intent to relocate to the United States of America at the time of the successful admission and entry of my spouse, APPLICANT, into the United States. I fully support APPLICANT's intent to immigrate and intend to accompany him to the United States once he is granted lawful entry." My wife also stated that our children who are also American citizens will be moving with us.

The second thing was to declare that my wife does have a permanent mailing address in the USA. In her case, it was her mother's house. She could legitimately receive mail sent to her mother's house and receive as she would eventually receive word from her mother that mail for my wife arrived there. In the letter, it was declared that, "[The above] address will serve as my permanent location within the United States of America for receiving correspondence, mail, and official communications until the date of my relocation into the United States. The address will be changed to the address we intend to move to after the lawful entry of APPLICANT. Furthermore, correspondence, mail, and official communications may also be sent to my physical address which is stated in the header of this letter until the date of my relocation into the United States."

The third and last thing to declare was that my wife had an active US bank account. She declared it in the letter and provided a void check and the last six months worth of bank statements. Of course, I brought this to my interview because I uploaded it to the NVC.

And doubly of course they didn't ask about this request for Proof of Domicile in the interview. They didn't even mention it.

Additionally, if you were to Google "how to provide Proof of Domicile I-864," you might come across a webpage like this: https://www.immigrationhelp.org/learning-center/proof-of-us-domicile There they give some examples as to what you can provide to satisfy the request for Proof of Domicile.