Why doesn't the player fall down?

I'm making my first mobile game on godot so I'm very inexperienced. It is a platformer. I would like the player, when he collides with the enemy, to fall down and die. I've been trying to do it for days, but it always gives me some different problem and I don't understand what I'm doing wrong. Could anyone help me please? I leave you the player code; in this way the player, despite having set velocity.y=.500, does not fall, but makes a sort of jump. What's wrong? Thank you all in advance.

PLAYER CODE:

extends KinematicBody2D
onready var rayS = get_node("rayL")
onready var rayD = get_node("rayR")
onready var sprite = get_node("AnimatedSprite")
var alive = true
signal dead
const WALK_FORCE = 600
const WALK_MAX_SPEED = 300
const STOP_FORCE = 1300
const JUMP_SPEED = 700
const gravity = 1100.0
var velocity = Vector2()
func _physics_process(delta):
var force = Vector2(0, gravity)
var walk_left = Input.is_action_pressed("move_left") and alive
var walk_right = Input.is_action_pressed("move_right") and alive
var jump = Input.is_action_pressed("jump") and alive
# Horizontal movement code. First, get the player's input.
var walk = WALK_FORCE * (Input.get_action_strength("move_right") - Input.get_action_strength("move_left"))
# Slow down the player if they're not trying to move.
if abs(walk) < WALK_FORCE * 0.2:
# The velocity, slowed down a bit, and then reassigned.
velocity.x = move_toward(velocity.x, 0, STOP_FORCE * delta)
else:
velocity.x += walk * delta
# Clamp to the maximum horizontal movement speed.
velocity.x = clamp(velocity.x, -WALK_MAX_SPEED, WALK_MAX_SPEED)
# Vertical movement code. Apply gravity.
velocity.y += gravity * delta
# Move based on the velocity and snap to the ground.
velocity = move_and_slide_with_snap(velocity, Vector2.DOWN, Vector2.UP)
# Check for jumping. is_on_floor() must be called after movement code.
if is_on_floor() and Input.is_action_just_pressed("jump"):
jumping()
var on_floor = rayL.is_colliding() or rayR.is_colliding()
if walk_right:
sprite.set_flip_h(false)
if walk_left:
sprite.set_flip_h(true)
if (walk_left or walk_right) and on_floor:
sprite.play()
elif (walk_left or walk_right):
sprite.stop()
sprite.set_frame(3)
else:
sprite.stop()
sprite.set_frame(1)
if position.y > 900: dying()
func _on_Area2D_body_entered(body):
if not alive: return
jumping()
body.destroy()
func jumping():
velocity.y = -JUMP_SPEED
func _on_Area2D2_body_entered(body):
if not alive: return
dying()
func dying():
if not alive: return
alive = false
velocity.y = -500
collision_mask -= 2
emit_signal("dead")

In 2D, the UP direction is negative on the y axis. Said another way, the Y axis is pointing downwards.

Thus, setting the velocity like this:

velocity.y = -500

Will result in upward motion, not downwards.

Addendum:

You can confirm that negative on the Y axis is upwards, and positive on the Y axis is downwards by looking at the definitions of Vector2.UP and Vector2.DOWN (documentation).

To make the player character move downwards, give it a downwards velocity. Which, to reiterate, is positive on the Y axis. For example:

velocity.y = 500

To reiterate: the UP direction is negative on the y axis and thus a velocity with a negative Y component moves upwards.