diff --git a/CRM/TwingleCampaign/BAO/TwingleApiCall.php b/CRM/TwingleCampaign/BAO/TwingleApiCall.php
index 010863d..b9f3c2f 100644
--- a/CRM/TwingleCampaign/BAO/TwingleApiCall.php
+++ b/CRM/TwingleCampaign/BAO/TwingleApiCall.php
@@ -25,7 +25,7 @@ class CRM_TwingleCampaign_BAO_TwingleApiCall {
    *
    * @throws API_Exception
    */
-  public function __construct($apiKey, int $limit = 20) {
+  public function __construct($apiKey, int $limit) {
     $this->apiKey = $apiKey;
     $this->limit = $limit;
 
@@ -116,7 +116,7 @@ class CRM_TwingleCampaign_BAO_TwingleApiCall {
    *
    * @return array
    */
-  public function getEvent(int $projectId, $eventId = NULL) {
+  public function getEvent($projectId, $eventId = NULL) {
     $result = [];
 
     $url = empty($eventId)
@@ -140,9 +140,12 @@ class CRM_TwingleCampaign_BAO_TwingleApiCall {
       $response = $this->curlGet($url, $params);
       $finished = ($eventId) || count($response['data']) < $this->limit;
       $offset = $offset + $this->limit;
-      if ($response['data']) {
+      if ($response['data'] && !$eventId) {
         $result = array_merge($result, $response['data']);
       }
+      else {
+        $result = $response;
+      }
     }
     return $result;
   }
diff --git a/api/v3/TwingleSync/Singlesync.php b/api/v3/TwingleSync/Singlesync.php
index 80fb41d..7483366 100644
--- a/api/v3/TwingleSync/Singlesync.php
+++ b/api/v3/TwingleSync/Singlesync.php
@@ -1,4 +1,10 @@
 <?php
+
+use CRM_TwingleCampaign_BAO_TwingleApiCall as TwingleApiCall;
+use CRM_TwingleCampaign_BAO_TwingleProject as TwingleProject;
+use CRM_TwingleCampaign_BAO_TwingleEvent as TwingleEvent;
+use CRM_TwingleCampaign_BAO_CampaignType as CampaignType;
+use CRM_TwingleCampaign_Utils_ExtensionCache as Cache;
 use CRM_TwingleCampaign_ExtensionUtil as E;
 
 /**
@@ -9,8 +15,28 @@ use CRM_TwingleCampaign_ExtensionUtil as E;
  *
  * @see https://docs.civicrm.org/dev/en/latest/framework/api-architecture/
  */
-function _civicrm_api3_twingle_sync_Singlesync_spec(&$spec) {
-  $spec['magicword']['api.required'] = 1;
+function _civicrm_api3_twingle_sync_Singlesync_spec(array &$spec) {
+  $spec['campaign_id'] = [
+    'name'         => 'campaign_id',
+    'title'        => E::ts('Campaign ID'),
+    'type'         => CRM_Utils_Type::T_INT,
+    'api.required' => 1,
+    'description'  => E::ts('ID of the campaign that should get synced'),
+  ];
+  $spec['twingle_api_key'] = [
+    'name'         => 'twingle_api_key',
+    'title'        => E::ts('Twingle API key'),
+    'type'         => CRM_Utils_Type::T_STRING,
+    'api.required' => 0,
+    'description'  => E::ts('The key to access the Twingle API'),
+  ];
+  $spec['is_test'] = [
+    'name'         => 'is_test',
+    'title'        => E::ts('Test'),
+    'type'         => CRM_Utils_Type::T_BOOLEAN,
+    'api.required' => 0,
+    'description'  => E::ts('If this is set true, no database change will be made'),
+  ];
 }
 
 /**
@@ -21,25 +47,80 @@ function _civicrm_api3_twingle_sync_Singlesync_spec(&$spec) {
  * @return array
  *   API result descriptor
  *
+ * @throws API_Exception
  * @see civicrm_api3_create_success
  *
- * @throws API_Exception
  */
 function civicrm_api3_twingle_sync_Singlesync($params) {
-  if (array_key_exists('magicword', $params) && $params['magicword'] == 'sesame') {
-    $returnValues = array(
-      // OK, return several data rows
-      12 => ['id' => 12, 'name' => 'Twelve'],
-      34 => ['id' => 34, 'name' => 'Thirty four'],
-      56 => ['id' => 56, 'name' => 'Fifty six'],
-    );
-    // ALTERNATIVE: $returnValues = []; // OK, success
-    // ALTERNATIVE: $returnValues = ["Some value"]; // OK, return a single value
 
-    // Spec: civicrm_api3_create_success($values = 1, $params = [], $entity = NULL, $action = NULL)
-    return civicrm_api3_create_success($returnValues, $params, 'TwingleSync', 'Singlesync');
+  $result_values = [];
+
+  // Is this call a test?
+  $is_test = (boolean) $params['is_test'];
+
+  // If function call provides an API key, use it instead of the API key set
+  // on the extension settings page
+  $apiKey = empty($params['twingle_api_key'])
+    ? trim(Civi::settings()->get('twingle_api_key'))
+    : trim($params['twingle_api_key']);
+
+  $twingleApi = new TwingleApiCall($apiKey, 1);
+
+  $campaign_type_id = 0;
+  $project_campaign_type_id =
+    CampaignType::fetch('twingle_project')->getValue();
+  $event_campaign_type_id =
+    CampaignType::fetch('twingle_event')->getValue();
+
+  $custom_field_mapping = Cache::getInstance()->getCustomFieldMapping();
+
+  $result = civicrm_api3('Campaign', 'get', [
+    'sequential' => 1,
+    'id'         => $params['campaign_id'],
+  ]);
+
+  if ($result['is_error'] == 0) {
+    if ($result['count'] == 1) {
+      $campaign_type_id = $result['values'][0]['campaign_type_id'];
+    }
+    else {
+      $count = $result['count'];
+      throw new API_Exception(
+        "Expected one Campaign but found $count",
+      );
+    }
   }
   else {
-    throw new API_Exception(/*error_message*/ 'Everyone knows that the magicword is "sesame"', /*error_code*/ 'magicword_incorrect');
+    throw new API_Exception($result['error_message']);
   }
+
+  switch ($campaign_type_id) {
+
+    case $project_campaign_type_id:
+      // Get a single project from the Twingle API
+      // TODO: Es darf nur ein Projekt sein! $result['values'][0][$custom_field_mapping['twingle_project_id']] pruefen! Sonst project pushen
+      $project = $twingleApi->getProject(
+        $result['values'][0][$custom_field_mapping['twingle_project_id']]
+      );
+      // Create project as campaign and store results in $result_values
+      $result_values['project'] =
+        TwingleProject::sync($project, $twingleApi, $is_test);
+      break;
+
+    case $event_campaign_type_id:
+      $event = $twingleApi->getEvent(
+        $result['values'][0][$custom_field_mapping['twingle_event_project_id']],
+        $result['values'][0][$custom_field_mapping['twingle_event_id']]
+      );
+      $result_values['event'] =
+        TwingleEvent::sync($event, $twingleApi, $is_test);
+      break;
+
+    default:
+      throw new API_Exception(
+        "Campaign does not belong to TwingleCampaign Extension"
+      );
+  }
+  return civicrm_api3_create_success($result_values);
 }
+
diff --git a/tests/phpunit/api/v3/TwingleSync/SyncTest.php b/tests/phpunit/api/v3/TwingleSync/SyncTest.php
new file mode 100644
index 0000000..3966106
--- /dev/null
+++ b/tests/phpunit/api/v3/TwingleSync/SyncTest.php
@@ -0,0 +1,53 @@
+<?php
+
+use Civi\Test\HeadlessInterface;
+use Civi\Test\HookInterface;
+use Civi\Test\TransactionalInterface;
+
+/**
+ * TwingleSync.Sync API Test Case
+ * This is a generic test class implemented with PHPUnit.
+ * @group headless
+ */
+class api_v3_TwingleSync_SyncTest extends \PHPUnit\Framework\TestCase implements HeadlessInterface, HookInterface, TransactionalInterface {
+  use \Civi\Test\Api3TestTrait;
+
+  /**
+   * Set up for headless tests.
+   *
+   * Civi\Test has many helpers, like install(), uninstall(), sql(), and sqlFile().
+   *
+   * See: https://docs.civicrm.org/dev/en/latest/testing/phpunit/#civitest
+   */
+  public function setUpHeadless() {
+    return \Civi\Test::headless()
+      ->installMe(__DIR__)
+      ->apply();
+  }
+
+  /**
+   * The setup() method is executed before the test is executed (optional).
+   */
+  public function setUp() {
+    parent::setUp();
+  }
+
+  /**
+   * The tearDown() method is executed after the test was executed (optional)
+   * This can be used for cleanup.
+   */
+  public function tearDown() {
+    parent::tearDown();
+  }
+
+  /**
+   * Simple example test case.
+   *
+   * Note how the function name begins with the word "test".
+   */
+  public function testApiExample() {
+    $result = civicrm_api3('TwingleSync', 'Sync', array('magicword' => 'sesame'));
+    $this->assertEquals('Twelve', $result['values'][12]['name']);
+  }
+
+}