Difference Between OPPV and IPPV - DirecTV

I am currently unable to order PPVs via my remote. In my research, it seems that IPPV must be enabled to do this but the CSR at Directv says that is incorrect and that OPPV should be enabled instead. I am curious as to the difference and which is correct. Thanks.

This question, "Difference Between OPPV and IPPV," is about DirecTV channels, programming, equipment, and sports.