Barter system works with a neighbor...but for millions of people? That'll be interesting.
Barter is very well established in international trade. Nealy all the largest banks do versions of that in very large transactions. Since most of it is quite large transactions and little of it involves direct regulated activity it tends to be invisible. Traditionally, over centuries, this has been a practice of factoring companies. The most traditional practitioners were Eastern European, principally Austrian and German, but nearly all worldwide Chinese/overseas Chinese communities are deeply involved with barter.
Why is that true and why does it remain largely invisible to the world? These transactions reduce nearly all transactions taxes that otherwise can be onerous. That is, the nominal financial value of barter transactions tends to be significantly less than would have been a monetary system. The practices are often multi-partate and frequently involve some parties who have "conventional trade restrictions" with each other.
Here is a brief description that vastly, repeat vastly, understates the use of barter:
The modern trade and barter industry includes three major sectors; traditional retail barter exchange companies, (also referred to as mutual peer-to-peer credit clearing systems), corporate barter companies, (who perform larger corporate barter transactions) and countertrade, (usually between...
www.irta.com
For major nations trading in commodities that can be somewhat fungible the practice of barter is very efficient for all concerned, especially if one or all parties are subject to trading restrictions with each other. In such situations multi-partate is typical, placing at least one neutral party between otherwise hostile parties.
There is not a large body of references about this business but there are some. All the good ones tend to trivialize the amount of barter in the world.
A few examples:
Major international airlines flying between countries with rigid trade restrictions, which tend to barter flights, aircraft furnishings, catering etc.
Commodity traders. Many source countries need specific products more than they need cash, so everything from barley, wheat. cotton, rice, to every precious metal. The destination countries tend to be industrialized or produce other desired commodities. Oil and gas, noble gases, and other raw materials are often traded with barter.
Candidly nobody knows how much barter there is but everyone who's ever had an direct exposure, however superficial, will understand it is far more prevalent than entrees like IRTA guesstimate.
I am no expert. I have worked on a few deals that involved places such as Sudan, Iran, and major western countries. In each deal I personally say there were multiple nationalities involved. Although not an expert, the experts I worked with were all from major global banks and all were part of large Trade Financing groups. The contracts and delivery processes are 'interesting' but generally do not have assigned monetary values placed on any part, often even shipping can be bartered.