Ember Selectbox select a child association in a form

Having trouble with selecting a belongsTo association to it's parent via a select box on an input form.

Model in question

export default DS.Model.extend({
  proNumber: DS.attr('number'),
  status: DS.attr('string'),
  special: DS.attr('string'),
  customer: DS.belongsTo('customer', { async: true }),
  carrier: DS.belongsTo('carrier', { async: true }),
  equipmentList: DS.belongsTo('equipment-list', { async: true}),
  stops: DS.hasMany('stop'),
  loadRates: DS.hasMany('load-rate'),
  grossPay: Ember.computed.mapBy('loadRates', 'rate'),
  totalGrossPay: Ember.computed.sum('grossPay')
});

Model that I'm trying to associate is customer above.

input - from Material - works exactly like most selectbox Ember addons

  {{md-select content=customerList
     value=model.customer  <-- doesn't work
     label="Customer"
     prompt="Please Choose a Customer..."
     optionLabelPath='content.name'
     optionValuePath='content.id'}}

The value doesn't work.