Serve faults and foot faults
A serve is a fault if it lands outside the box, is hit above the waist, is missed, hits your partner or breaks a foot rule. Two faults in a row lose the point.
The faults
A serve is a fault when: it bounces outside the receiver's box (the lines are in); it is hit above the waist; you swing and miss; it hits you, your partner or anything either of you carries; it hits the receiver's wall or mesh before bouncing; or it touches the mesh after bouncing in the box.
Foot faults
Your feet must stay behind the service line and on your side of the imaginary line running back from the centre line until you hit the ball. Do not touch either line, and keep at least one foot on the ground at contact. Walking or running into the serve is not allowed.
The bounce
Bounce the ball behind the service line, within your own half, before you hit it. Hitting the ball out of the air, or bouncing it in front of the line, is a fault.
Second serve
After a fault you serve again from the same side. Two faults in a row lose the point. If a mistake in the order is found, a single fault already served still counts.
Questions
Is it a fault if I touch the line when serving?
Yes. Stepping on the service line or the centre line while serving is a foot fault.
Can you jump when serving in padel?
No. You must have at least one foot on the ground when you hit the ball.