I think what
@Hangover is saying is this:
The Order Agreement is essentially your bill. In accounting terms, these are debits. Here's a hypothetical Order Agreement/bill below, assuming one ordered in mid-May.
LR AWD: $51,990
White paint
19"
Black
Five Seat
AP
Tow: $1,000
Destination: $1,200
Order Fee: $100
------------------------
Total: $54,290
Immediately prior to taking delivery, they generate a final amount due statement. It'll show how much you already paid, and how much you still need to pay to settle the full bill. The $100 already paid will be listed as a "credit" (again, in accounting terms), but it's not a customer credit or gift from Tesla, as we might think in customer service terms. It notes that it was an amount paid to go towards settlement of the final bill, but it was still part of the bill nonetheless.