It might be prudent to note that "cash" has meaning in the context of electronic payment research, going all the way back to DigiCash in the 90s. That system required a trusted third party to operate, but it was still cash in the sense that it is a transfer of value, not debt. The way most payment systems operate is that they are settled at a later date (in some cash equivalent). In that sense, credit card payments as well as Venmo are layer 2 solutions.