Right. That is a good point. Although Marx didn’t see the elimination of currency as a realistic goal attainable within the first few decades (possibly even the first century) of communism, he did believe a post-scarcity humanity would eventually transcend the need for currency.
However when it comes to barter, the thing is: even in societies dominated by barter, some commodity tends to become the standard against which the values of other commodities are measured. Cigarettes in POW camps, cacao beans in Mesoamerica.
By an admittedly-loose definition of currency, a currency does always emerge and end up being directly exchanged for goods and services, even in barter systems.