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
TurboTax does not know why you did not receive the CTC payment. It is possible that your payment has not posted to your account yet, or that they mailed a check and you need to watch your mailbox. If your 2020 return or an amended return is still pending you will not receive a monthly advance check.
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.
DO NOT use the Non-filer Sign-up Tool if you filed a tax return. It will just cause more problems. The Non-filer Sign-up Tool is only for people who "are not required to file a 2020 tax return, didn't file one, and don't plan to."