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.
If you filed the 2020 return and it has not been fully processed yet then that could be why the portal is giving you that message.
According to the IRS if your return, even an amended one is still processing then you will not receive the advance child tax credit payments. Go to topic Q B 12 as of June 30th there were 35 million US income tax returns that had not been processed and estimated only 3% of phone calls were being answered. Verify that here