Cannot create new Activerecord with belongs_to relationship - ruby-on-rails

Question

I am a beginner with Ruby on Rails and I am trying to create a seed.rb file to populate my database.
However I am having problems creating a new Request record.
This is my seed file:
if Rails.env == "development" || Rails.env == "test"
avaya = Company.create!(name: "Avaya")
microsoft = Company.create!(name: "Microsoft")
bradesco = Company.create!(name: "Bradesco")
customer = Customer.create!(name: "Leon Schmidt", email: "leon.schmidt#avaya.com", company_id: avaya.id)
Customer.create!(name: "Teri Wright", email: "teri.wright#avaya.com", company_id: avaya.id)
Customer.create!(name: "Jasmine Bush", email: "jasmine.bush#microsoft.com", company_id: microsoft.id)
Customer.create!(name: "Jake Blair", email: "jake.blair#bradesco.com.br", company_id: bradesco.id)
rate = Rate.create!(rate: 0.0165, days: 10, default_rate: true)
Request.create!(title_value: 1500, term: 28, monthly_revenue: 75000, receivable_value: 1425.75, rate_id: rate.id, customer_id: customer.id)
elsif Rails.env == "production"
Rate.create(rate: 0.0165, days: 10, default_rate: true)
end
Whenever I run rake db:reset to repopulate the development database I get this error:
rake aborted!
ActiveRecord::RecordInvalid: Validation failed: Customers must exist
c:/Desenvolvimento/Coding Tests/FactoringRateCalculator/db/seeds.rb:23:in `<top (required)>'
Tasks: TOP => db:reset => db:setup => db:seed
Please note that the line 23 is: Request.create!(title_value: 1500, term: 28, monthly_revenue: 75000, receivable_value: 1425.75, rate_id: rate.id, customer_id: customer.id)
My models are below:
class Customer < ApplicationRecord
belongs_to :company
has_many :requests
validates_associated :requests
validates :name, presence: true
validates :email, presence: true, email: true
end
class Request < ApplicationRecord
belongs_to :customers, required: true
belongs_to :rate, required: true
validates :term, presence: true, numericality: { greater_than_or_equal_to: 10 }
validates :title_value, presence: true, numericality: { greater_than_or_equal_to: 500 }
validates :monthly_revenue, :receivable_value, presence: true, numericality: true
end
class Rate < ApplicationRecord
has_many :requests
validates_associated :requests
validates :rate, numericality: true, presence: true
validates :days, numericality: { greater_than_or_equal_to: 10 }, presence: true
validates :rate, :days, :default_rate, presence: true
end
class Company < ApplicationRecord
has_many :customers
validates_associated :customers
validates :name, presence: true
end
I am using Ruby 2.3 and Rails 5.1.

Answer 1

Your required validation is specified with the plural version of your model:
belongs_to :customers, required: true
Try using the singular way:
belongs_to :customer, required: true
That's why the error says "Customers": "ActiveRecord::RecordInvalid: Validation failed: Customers must exist", because your seeds have been made following the relationship you specify.