Cover 1858 Single Stamps To Italy Rome

Good morning
I wanted to ask the mail experts why the letter is free with a value of only 12 cents for Italy

Stamps are clearly missing. Note how the Charleston cancels abruptly cut off?

is the corner folded the envelope is not in excellent condition

Someone tore off the stamp that was at UR.
The french treaty rate to Rome I believe was 27c.

Rome is a great destination at this time, it still being a Papal state.

Probably right, but the envelope is taxed 15 if I'm not mistaken

This cover was carried on the Havre line Steamer "Arago" which Left NYC on August 21, 1858, and arrived in Havre on Sep 2.

The combination of PAID in the NYC exchange, the French "PD", and the large slash, indicate that it was fully paid through to Rome.

The 15 is a credit. (to France- 3c inland postage, 12c transit to Rome)

Two stamps are missing: A 3c stamp, probably a #26, and another 12c stamp. A spot for each may be found as follows:
- at the upper right corner, where one was torn away
- immediately to the right of the 12c stamp on cover, where the CDS is short