Where the per-text money actually goes. The carriers charge for every message, and those costs pass through the plans.
Every SMS crosses a carrier network, and every carrier charges for the crossing. Those fees are set by the carriers, not by Txtra, and they're the largest single cost inside your plan rate.
10DLC political registration carries one-time and recurring carrier fees. Txtra files the registration and the plan absorbs the standard costs. Short codes are different, mostly carrier pass-through from about $1,200 a month, which is why they're priced apart.
Carriers bill per SMS segment. A long message or one with media counts as more than one, which is why your allowance counts segments too. RCS on supported handsets doesn't carry per-segment math, one reason the platform is RCS-first.
Carriers adjust fees, sometimes mid-cycle. Plan rates hold for your term. If the underlying costs move enough to reprice a tier, the change lands at renewal with notice, never mid-term.