module controller does not respond!
You forgot requirements (which is required):

my_module.agreement:
  path: 'my_module/send_consent'
  defaults:
    _controller: '\Drupal\my_module\Controller\MyModuleController::check_agreement'
    _title: 'Agreement controller'
  methods:  [GET]
  requirements:
    _permission: 'access content'


See Structure of roots for full details.