It is actually asking you for your Robinhood account number.
If you are experiencing problems while importing from Robinhood, " In TurboTax, when prompted to “Choose your bank or brokerage,” enter “Robinhood” in the search field. TurboTax will ask for your account number, which can be found in the Tax Documents section of the Robinhood app. Please add "10-" before the first 8 digits of your account number (10-5XX12345). Do not include hyphens in your SSN."
You may experience difficulty uploading your Robinhood financial transaction history into TurboTax if you made close to 500 transactions in 2016. TurboTax Online can handle up to 500 transactions per brokerage account. However, online performance may deteriorate as you get close to this limit. For more information about this, or if you made more than 500 stock transactions, please see instructions here.