You can't put your finger on it because money is merely an accumulator and medium of exchange of economic performance. The performance of services in exchange for other services without money is a perfectly valid economic exchange that can and should be booked to revenue of each of the parties, if actually performed.

Loans without any economic performance of services generate circular meaningless cash flows yeah, but that's not the case when services are actually performed.

Loans are promises to pay. Business deals are promises to perform services or deliver goods. The difference is easily lost in the details even for accountants and economists.

That's a bit jumbled. You can gain clarity one level up the abstraction layer. Money is a note that means a debt is owed.