If you receive SSI---and do not get a SSA1099---you can use this portal on the IRS site:
IRS PORTAL FOR NON-FILERS
https://www.irs.gov/coronavirus/non-filers-enter-payment-info-here
Confusion results when people refer to Social Security benefits as "SSI" because they are not the same thing and are not paid in the same way--especially for the stimulus money.
WHAT IS THE DIFFERENCE BETWEEN SOCIAL SECURITY BENEFITS AND SSI?
https://www.ssa.gov/ssi/text-over-ussi.htm