Rinnai tankless water heater

I have a RXP199in and purchased a flexible gas line that is Yellow Epoxy Coated 3/4"MIP x 3/4"FIP (1"OD) Full Flow,High Btu,Flexible Gas Connector Hose Supply For Commercial,Residential. The fittings are too big for the unit. The manual calls for 3/4" NPT. What flex line can I use?