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
