Degrowth

It should be noted that anarcho-syndicalism is the only flavour of anarchism that has needed to supply anarchist units fighting a war (Spanish Civil War), and to raise foreign currency by exporting what it could, during a time of economic trouble - and it could do that.

Their system? Representatives from different plants regularly convened, discussed the inputs and outputs of their production, made agreements and resolved disputes. There was a market, a more transparent market than capitalism can provide - and the actors on this market had a democratic mandate from workers. Sometimes they traded for money, sometimes they exchanged services or goods for other services or other goods... sometimes they simply helped each other out (a step that's ridiculously hard to perform in capitalism).

However, there was also a government in the background - fighting on the same side as anarchists, with no power to spare for cracking down on syndicalism until much later.

I wish I knew what they did when some plant became indebted to another or failed its promises. I don't know if historians have written about it.

As for scaling - yes, transparency and trust don't scale infinitely. If the partner in a deal is distant in some way (geographically, politically, otherwise), one may not want to discuss everything with them. Thus, when a syndicalist company trades with a non-syndicalist company, they probably don't show their cards.

P.S.

A note about communications: the Barcelona telephone exchange continued to operate under anarchist control in the aforementioned situation. If they needed capacitors, resistors, lamps, speakers, relays or wire, I'm sure some other worker-controlled company could make those. Of course, Internet was not a thing back in the 1930-ties.

BBS-es and FidoNet existed on top of the telephone network before the Internet became a thing. BBS-es were largely amateur run dial-in servers and there was no central authority to steer their development. Fidonet was a standard, but nobody with authority stood behind it. Of course, its users were mostly DIY technology enthusiasts and weren't moving money, so much of the problems we encounter on the Internet (scams, ads, DRM, etc) were unknown of. Fidonet was not a "well run network", however - since long distance call rates placed a burden on node operators and even caused infighting.

Radio amateurs set their standards and started global communication without a central authority, states regulated their activity (with permits and punishments for violations) only later.

I very much doubt if we'd not have an Internet on an anarchist planet. I think we'd have a different Internet.