It's been a long time since I bought on TD directly from a bank account, so I don't have the answer.
I do know if you don't have enough in your C&I, it fails and they send you a message.
So you may ask, "Joe how do you know this?" Well, what happened was I attempted to buy a TIPS a few years ago. I had 10k in my C&I and bought a TIPS for $10k. It failed because the TIPS were at premium at the time and needed more than $10k.
Now that I've learned how to buy Treasuries on Vanguard, I'm done with TD for all except iBonds. I'll be rolling out the money as the securities mature.