Jump to S10 from S9 and still take advantage of $390 for trade in

I haven't found the answer to this yet. I owe $360 on my S9, but am halfway through and am eligible to jump to a new phone. I see there is a $390 trade in for S9 in the form of bill credits.

If I jump to the s10, can I use the s9 as the trade in or does the s9 need to be totally paid off in order to use it as a trade in?