Salt was also one of Spains biggest exports in the 1500s and had been so for many centuries.
Prior to that most European countries were on one or the other of gold or silver. This got derailed by the arrival of huge amounts from the New World.
My understanding was, even being on precious metals, most trading happened on the goods, not the metals. Mostly for predictable reasons on the supply chain not being nearly as efficient at moving goods away from producers. That not accurate?
I'm not sure what this means? There were definitely goods-goods exchanges on infrequent or first-contact routes, such as the early settlers of the Americas, but Rome had a fairly sophisticated set of concepts such as trade credit and instalments, and Europe recreated this in the Renaissance. Banco MPS dates from 1472, remember.
So while you'd generally see "on the nail" money-goods exchanges, the set of individuals doing trading would be small and known to each other, making credit available.
Code of Hammurabi, 4000 years old, makes some stipulations for how trade credit and agents should work, see rule 100 and onwards https://avalon.law.yale.edu/ancient/hamframe.asp
You can also only consume so much salt without dehydrating yourself.
The people of the southwest struggled with other nutritional deficits though. Lysine deficiencies, anemia, and scurvy were all present at fairly high rates throughout the population, especially in children.
I suspect the person sharing this sees some parallels with the current political resistence over the sale of salt flat lands to lithium mining companies in Utah [0] and Chile [1].
[0] https://www.npr.org/2023/07/17/1188204958/tribes-object-fede...
[1] https://www.youtube.com/watch?v=_PWrsTjMzhs&pp=ygUYYWwgamF6Z... (25 min)