For me BOI asked for the same documents referenced in the letter above attached to the post by Jim Ramsey. Hopefully you have been retired for all/most of 2024.... Your last tax return (ie 2024 1040) will normally be required.
As in the post above Ramsey post, be sure to include tax free income that does not appear on your tax return. For example, dividends and capital gains in any Roth accounts (those helped put me over the $80k mark).
I've used Google Voice 6 years. Free. Great for calling toll free numbers, friends, SMS verifications. Set it up before you go because I think setup requires verification through another US phone # .
The IRS 1040 does not include Roth IRA dividends (or if I remember IRA 401K dividends?). You can also in a tax year take a larger IRA distribution or sell some stocks for capital gains to possibly go over the 80K. But check with ExpatTax or other experts.