To connect your TD Ameritrade account to Option Alpha, go to Settings --> Trading Accounts and select 'Authorize on TD.Ameritrade.com.'
You will be re-directed to their website to log in using your TD Ameritrade username and password.

Once your accounts are connected you can select your TD Ameritrade account when creating a new bot to trade live.
You can authorize one set of credentials (username/password) per broker. You can connect multiple accounts with the same username.
If your TD Ameritrade account has 'Advanced Features' or 'Auto Position Effect' enabled, your account will be labeled 'Incompatible.' Learn more about Incompatible Accounts.