The serve must be underhand and below the waist
Padel rules · Serving
In padel you serve underhand. You must bounce the ball once on the floor behind the service line, then strike it at or below waist height (roughly hip level). Contact above the waist is a fault. The serve is hit diagonally into the opposite service box and the ball may then touch the side glass of that box, but not the metal fence.
📘 Category: Serving. This is one of the rules that most often confuses players coming from tennis or pickleball.