As I said, the Confederates ordered arms they could not pay for when delivery day arrived, and these were sold to whoever in the world wanted them and could pay for them. This is clearly documented.
There was plenty of credit in those days. It wasn't MasterCard or Visa, it was in the form of Letters of Credit. A buyer would negotiate with a seller, and the buyer would try to put down the lowest acceptable deposit and agree to pay the rest on delivery, or, better yet, to pay another partial payment upon delivery and the balance later. No buyer would pay the full price in cash when ordering arms in 24 bore or 25 bore - just imagine writing back to your employer and telling them you had spent all the money you had, you had no arms yet, but you expected some British company to deliver them a few months! Such a buyer's agent would be fired on the spot.
Confederate inspection marks were put on in Britain, before the arms were paid for and loaded into ships. So rifle muskets made intentionally in 24 bore which have confederate inspection aka viewer's marks were inspected by confederate viewers and accepted for confederate purchase even though made in the Union 24 bore standard size. There's more than a few 24 bore Enfields in collections which also have confederate viewers' acceptance marks applied in Britain - so, made in the Union caliber of 24 bore, but inspected by confederate inspectors after made.
I think both sides would buy Enfields in either 24 bore or 25 bore in the earlier part of the War, whichever was available to them on the market.