RC6

kirby/config/api/models/System.php

@@ -64,6 +64,7 @@ return [
     'views'  => [
         'login' => [
             'isOk',
+            'isInstallable',
             'isInstalled',
             'title',
             'translation'

kirby/config/api/routes/system.php

@@ -53,6 +53,10 @@ return [
                 throw new Exception('The server is not setup correctly');
             }
 
+            if ($system->isInstallable() === false) {
+                throw new Exception('The panel cannot be installed');
+            }
+
             if ($system->isInstalled() === true) {
                 throw new Exception('The panel is already installed');
             }