What was wrong with money? The cotton exporter sells to sources in Britain. The British exporters sells to sources in New York. No need to barter.
I guess there was nothing wrong with money, but I would assume that the hassle of securely transporting large sums as opposed to simple notations on a ledger favored the latter system. The same reason actual money doesn’t get transferred every time you swipe a debit card.
“Cotton was the only cash crop. It was moreover the only crop which could be used as a basis of credit.”
From the Cotton Factorage System of the Southern States, Alfred Holt Stone, Oxford University Press
https://www.jstor.org/stable/pdf/1835857.pdf