Connectedness commerce relies on buildings and the first general building is the Caravanserai, which is not available until the early Classical Era. The first transition should come well before that.
I'm thinking of ideas for what to do about the Ancient Era economy. I definitely want there to be something between Barter and Coinage.
Eh, I mean, economics is kind of an oddball category, is there really anything wrong with that?
In terms of game design, as long as everyone is stuck with Barter until Coinage then there is no advantage given to anyone, no fault there. In those same terms, as long as the difference between Barter and Coinage is a relative benefit that scales over time then the unlock tech Currency will not be overvalued or warp the surrounding tree, so no fault there.
In terms of history, which is somewhat relevant to this game, I dont think there really was any identifiable extra stage between Barter and Currency, and for a lot of the history of barter trade was done with a commodity money anyway, frequently of precious metals or grain of regulated weights. In the places where where Coinage has emerged independently a token currency of metals already existed, the main transition was just in production and stamping etc and ofc some conceptualization.
If for whatever reason ensuring that the Economics category has an extra gimp civic that exists only to switch away from is an imperative; I could instead mention the theories that early tribal economies more likely did not even operate on the basis of Barter, but rather on the basis of what I think is mostly known as a Gift economy, sharing is caring. The main distinction being that barter is a transaction, it has immediacy, the gift economy operates on trust and community, thus you can give to your neighbor today and they if able may give to you next year, but not in a necessarily formalized manner. This obviously had serious issues operating beyond a single tribe or community. Barter supposedly first existed between heads of tribes to exchange whatever specialized resources the tribes had to trade, then became more prevalent down the social strata as wealth increased both the means and need for it.
Thus, rather than inventing a transition between Barter and Coinage, Barter could be the transition between an earlier civic and Coinage.
Idk if any of that is helpful to you, but if you're working on ideas that might be a place to start.
... but I will say this. Foreign commerce penalties are not going to be part of the Barter civic because there is no foreign commerce at that point to penalize. Foreign trade does not work the same in AND as it does in BTS; city connections don't give any commerce on their own. Connectedness commerce relies on buildings and the first general building is the Caravanserai, which is not available until the early Classical Era. The first transition should come well before that.
I did in fact understand that there were different

mechanics than in BTS and that Foreign

is irrelevant in the Ancient Era, that was part of the point. I did not necessarily see the need for the 1st Economy civic to be a gimp that exists only to be switched away from in the Ancient Era. I see no basis for that philosophy, there are plenty of other categories that do not operate by that philosophy and as far as I can tell are not harmed thusly. Certainly there are a number of Civics that should be deincentivized at some point for historical reasons, but the when, how and why is important. Therefore since I saw no reason that the player should be forced out of Barter in the Ancient Era I thought that a penalty to Barter that only became relevant in following Eras when Barter did in fact cease as the main method of exchange seemed appropriate.
The other part of the point was that currently** the transition between Barter and its 1st alternative, Slavery, is not at all subtle, thus I thought that having the transition between Barter and Coinage
(when slavery is removed as an intermediate) being subtle would be a good thing. In the period of the game where Currency is unlocked most civs are both building that early

building the infamous Caravanserai as well as expanding; thus the power of

both Foreign and Domestic, begins to increase, but in a gradual way. A choice that is too obvious is a non-choice. Since I believe we are forced to discourage use of Barter in later Eras for good reason, I thought that the choice could be not
if to switch, but exactly
when to switch. The components of that choice that I thought would be interesting were the opportunity cost of Anarchy against some kind of relative +%


from Coinage to Barter and for flavor the gradually increasing importance of

.
The third part of that point, which is less important to some than others, is that historically part of the incentive of switching from barter to coinage was the literal currency it afforded in foreign trade. This is of course a game, but when mechanics can so readily match their historical counterpart should they in fact not?
All of this reasoning is of course irrelevant if we are operating under the unbendable premise that Barter must be abandoned in the ancient era, which I was not when I reasoned my reasoning.
**currently, in rev1066 and previously, the gap between Barter and the 1st alternative to it is Huge, switching from Barter to Slavery is a 66% increase in


, almost entirely just because the penalties to Barter are so extreme. That kind of a relative increase in economic power would be insane anywhere else in the tech tree, if anyone hasnt noticed it I assert it is only because so early in the game almost every single tech has some kind of huge relative value.