The barter system is a myth, it never existed. Not in the 'I want bricks but only have a sheep and you don't want a sheep so we both get nothing' way that it's taught in highschool econ class.

Before cash, trade could use items of high constant demand - salt, cacao beans, dried tea, etc. - as a medium of exchange. Maybe you're fine for salt, but someone will always want more salt. It was also much more common to just rely on debt. Sure, take my extra bricks and when you have something of equivalent value that I want, you discharge your debt.