Multiple checkbox values are saved but not loaded in Rails form

My app has merchants that can accept 3 methods of payment. In order to create / edit the records I am using multiple checkboxes in a form and an array field in PostgreSQL

The funny thing is that it works fine when saving the values, both when creating and updating. The array is saved fine in PG based on the checkboxes values. However, when editing, the checkboxes do NOT load the correct values from the database. They all appear unchecked. The same thing happens when creating even with the default values as supposedly checked.

Any help would be appreciated.

Shared view partial for create and edit:

= form_for @merchant, layout: :horizontal do |f|
  = f.check_box :payment_accepted, { :multiple => true }, 'Credit Card', nil
  = f.check_box :payment_accepted, { :multiple => true }, 'Paypal', nil
  = f.check_box :payment_accepted, { :multiple => true }, 'Direct Deposit', nil
  = f.submit 'Save Changes', :class => 'btn btn-primary'

My controller code is:

class MerchantsController < ApplicationController
  load_and_authorize_resource
  before_action :set_merchant, only: [:show, :edit, :update, :destroy]

  respond_to :html, :json, :js

  def index
    @merchants = Merchant.all
  end 

  def show
  end 

  def new 
    @merchant = Merchant.new
  end 

  def edit
  end 

  def create
    @merchant = Merchant.new(merchant_params)
    @merchant.save
    respond_with(@merchant)
  end 

  def update
    @merchant.update(merchant_params)
    flash[:notice] = 'Merchant was successfully updated.'
    respond_with(@merchant)
  end 

  def destroy
    @merchant.destroy
    redirect_to merchants_url, notice: 'Merchant was successfully destroyed.'
  end 

  private
    def set_merchant
      @merchant = Merchant.find(params[:id])
    end 

    def merchant_params
      params.require(:merchant).permit(:name, :description, :notif_email, :category_id, :country_id, :costo_procesamiento, payment_accepted:[]) 
    end 
end

And my migration:

class CreateMerchants < ActiveRecord::Migration
  def change
    create_table :merchants do |t|
      t.string :name
      t.text :description
      t.text :default_terms
      t.text :notif_email
      t.boolean :visible, default: true
      t.integer :category_id
      t.integer :country_id
      t.integer :costo_procesamiento, null:false, default: 0
      t.string :payment_accepted, array: true, default: "['Credit Card','Paypal','Direct Deposit']"
      t.references :country, index: true, foreign_key: true
      t.timestamps null: false
    end
  end
end