My form doesn't submit

Hi,

My form keeps giving me a error on submit, i don't know what the problem is?

My form .yaml file:

title: Economie
fields:
  merk:
    display: 'Beschrijf uw merk'
    type: textarea
  current_website:
    display: 'Uw huidige website'
    type: text
  example_websites:
    display: Voorbeelden
    type: textarea
  blog_portfolio:
    display: 'Pagina | portfolio of blog'
    type: number
  custom_design:
    display: 'Pagina | Custom design'
    type: number
  content_page:
    display: 'Pagina | Content page'
    type: number
  animated_pages:
    display: 'Options | animated pages'
    type: checkbox
  mailchimp_intergration:
    display: 'Options | mailchimp intergration'
    type: checkbox
  hosting:
    display: Hosting
    type: radio
  domein:
    display: Domein
    type: radio
columns:
  - blog_portfolio
  - custom_design
  - content_page
  - animated_pages
  - mailchimp_intergration
  - hosting
  - domein
email:
  -
    to: [email protected]
    from: cornelius
    reply_to: [email protected]
    subject: onderwerp

All the fields match with the input name's, what can be the problem?

Thanks in advanced!