Paper Currency Is The New Gold

I have a deal with my colleague Jay. About 2 or 3 times per week, he picks up breakfast for me on his way into the office. In exchange, I pay for his breakfast on those days. When he hands me breakfast (usually a platter of eggs, bacon, and sausage) he tells me how much I owe him. I find this annoying, because I have to fish out cash from my wallet. Often we don't have the exact amount, or I just don't have any cash on me at all.  It would be really great if Jay were on Venmo, the excellent app...