Trade-in offer costed me more?

I had this same question with a similar promotion (slightly different numbers, but the same issue). 

In my case: iPhone 11 trade in valued at $190. New ("free") iPhone 13 costing $800.

So $800-$190 credit was $610 remaining, which over 24 months came to a $25 credit each month. That left $8 each month, which was billed to me.

That all made sense when phrased that way. But here's where I was getting confused:

If I received $190 initially but also end up paying $190 over 24 months, wasn't that a wash? So I didn't receive 190 (whether it paid my bill or my equipment is irrelevant) if I ended up paying 190.

0 + 190 - 190 still equals 0, whenever and however the 190 was applied or charged.

So then my credit was really just the $610 ($25 monthly x 24 months). 

Then I (think) finally figured out where the confusion came in: the promotion is not a free iPhone PLUS the fair market value of the phone. You don't actually get to pocket the fair market value of the phone AND get the full price of the new phone credited to you.

It’s a free iPhone AFTER the fair market value of the phone is subtracted.

I think that finally makes sense to me...