One possibility, and the more popular one, is to introduce a cash-in-advance constraint i.e. a requirement that each consumer or firm must have sufficient cash available before they can buy goods.
Without these (or similar) assumptions economic theory would find it difficult to explain why people carry around a good (money) which takes up space in their wallet, can't be consumed and does not earn any interest.
In actual daily business these sort of terms are extremely rare unless the goods or services are of phenomenal value and high fragility.
In these modeling theories, CIAC tends to show that up-front restrictions artificially limit the ability of companies to maintain positive inventory levels while reducing capital investment.
They also inhibit real wealth in terms of cash on hand while elevating the likelihood of using junk bonds as instruments of solvency, a dangerous premise.