The Spanish side will pay Liverpool €5m (£4.5m), after Philippe Coutinho won the Champions League with Bayern Munich on Sunday night.
The winger came on as a second-half substitute as the German club defeated Paris Saint-Germain 1-0 in Lisbon, Portugal.
The Brazilian who is on loan at Bayern, moved to Barca from Liverpool for a fee around £142m in 2018.
After a disappointing form with the LaLiga side, he moved to the Bundesliga team, where he has now helped them win a Treble this season.
Coutinho scored twice against his parent club, Barcelona, during the 8-2 thrashing last Friday.
The deal to sign Coutinho from Liverpool included a number of potential add-on clauses and interestingly, they are player-specific not club-specific.
One of those clauses was that Barca would pay Liverpool €5m if the 26-year-old won the Champions League in either the 2018/2019 or 2019/2020 season, but it does not specify that it had to be while playing for them.