Section 5: Rules of Play

A match is played as best of 3 sets: Sets 1 and 2: First team to 21 points wins, with a minimum 2-point advantage required (no cap — play continues until one team leads by 2) (Rule 6); Set 3 (deciding set): First team to 15 points wins, again with a minimum 2-point advantage (Rule 6); Sets 1 and ...

Source: Rule 6, Rule 18.2, Rule 12, Rule 9, Rule 13, Rule 15.4

Send this to your friend — argument over.