fix display error message (#293)

Co-authored-by: Julien Nahum <julien@nahum.net>

client/components/pages/pricing/CheckoutDetailsModal.vue

@@ -83,7 +83,7 @@ export default {
         opnFetch('/subscription/new/' + this.plan + '/' + (!this.yearly ? 'monthly' : 'yearly') + '/checkout/with-trial').then((data) => {
           window.location = data.checkout_url
         }).catch((error) => {
-          useAlert().error(error.response.data.message)
+          useAlert().error(error.data.message)
         }).finally(() => {
           this.loading = false
           this.close()