I noticed that addition too. I know RPP stands for Receiving Party Pays, but did not have the time to investigate it further.
Not sure of the minimum charge thing. May be that's why they charge for calls that did not complete/busy. They even list it as busy line on the website than list a charge next to it.

My busy calls were each charged between $0.31 and $0.50. The SMS were each charged at $0.80. According to the rates these should have been $0.30.
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile