On the 2020 return if you had no earned income (disability doesn't count) then you got no CTC on the return and the advance was being sent out based on the 2019 or 2020 returns. If you don't get it in advance then you will get the credit on the 2021 return if you have any qualifying income.
https://www.irs.gov/credits-deductions/advance-child-tax-credit-payments-in-2021
