We cannot see any of your information so we do not know what the portal is telling you or why it says you are not eligible yet. This is a brand new system thrown together by the IRS after Congress changed tax laws in the middle of the tax season. There are going to be bugs, glitches and mistakes made and folks will unfortunately have to be patient until they sort it out.
If you do not receive the monthly payments you will be able to get the CTC on your 2021 tax return.
https://www.irs.gov/credits-deductions/2021-child-tax-credit-and-advance-child-tax-credit-payments-topic-a-general-information