Most likely it's too early ... usually this is not functional until mid February at the earliest ... check with the broker to find out when the import will be operational. And watch out ... if your account usually gets corrected statements it is best to wait for them before filing so you don't need to amend later.
See this TurboTax support FAQ for importing 1099's - https://ttlc.intuit.com/community/entering-importing/help/how-do-i-import-my-1099/01/26254
I'm having the same issue as of February 27, 2020. I've received the 1099 composite paper copy from Charles Schwab a few days ago and the electronic copy was available over a week ago from the Charles Schwab site. I would prefer not to manually enter dozens of trades when the download feature will do that for me. Is this a glitch in Turbo Tax? It would be helpful if Turbo tax can update their download screen to indicate the anticipated date for this option to become available. It currently says "Some forms will be available after 2/19/20." Charles Schwab is a huge financial player. Perhaps a turbo tax person can contact them and get an accurate date for all of us users as opposed to suggesting the masses reach out to them individually.
If the amount of transactions is over 1500, you will not be able to import them. The other option would be to use the
TurboTax CD/Download software, which can handle up to 2,000—2,500 transactions.