The most usual ways to pay online when buying something on the internet is using a credit card or online money transfer providers (i.e., PayPal, Stripe). The telematic communication makes logical that payments methods are always electronic.
However, some companies have developed systems to provide payment with cash for electronic transaction. You can find some examples below.
YesByCash
https://www.yesbycash.com/
Supported by TSI Payment (France).
PaySafe Cash
https://www.paysafecash.com
Supported by PaySafe Group (UK).