The coffee is on me.
KAF-feh lo OF-fro EE-oh. 'offro' = to offer/treat. Very natural and warm Italian expression.
Use at the end of a meal when you want to treat your companions to the post-meal coffee. This is a very common Italian social gesture.
'Lo offro io' = I offer it / it's my treat. 'Lo' is a direct object pronoun referring to 'il caffè'. The structure 'lo + verb + io' is emphatic — putting 'io' at the end gives extra force ('I offer it, specifically me').
Offro il caffè a tutti.
I'm buying coffee for everyone.
Extending the offer to the whole table.
Questo giro lo pago io.
This round is on me.
More general — can apply to any round of drinks.
Ho già pagato il caffè.
I already paid for the coffee.
Informing others that coffee is settled.
Post-meal coffee is sacred in Italian culture. An espresso after lunch or dinner is a ritual, not optional for many Italians. Offering to pay for the coffee ('offro io il caffè') is a warm gesture that closes the meal socially. It's worth approximately €1-1.50, but the gesture carries much more weight than the amount.