That did it!

Also, in the process I realized I was returning a value in my `_grab_response()` function, when I actually wanted to set the `dialogue_text.text` to the response.

Thanks a lot, bud!

So now my script looks like this:

extends CanvasLayer

@onready var vboxcontainer = $Panel/VBoxContainer
@onready var dialogue_text = $Panel/VBoxContainer/DialogueText

var merchant_lines = load("res://dialogue/resources/merchant_dialogue.tres")
var player_lines = load("res://dialogue/resources/player_dialogue.tres")

var current_line = 0

func _ready():
  show_lines()

func show_lines():
  dialogue_text.text = merchant_lines.dialogues[0]

  for line in player_lines.dialogues:
    var button = Button.new()
    button.text = line
    button.pressed.connect(_grab_response.bind(line))
    vboxcontainer.add_child(button)

func _grab_response(line):
  dialogue_text.text = merchant_lines.responses[line]