diff --git a/classes/local/backup/restore_lifecycle_workflow.php b/classes/local/backup/restore_lifecycle_workflow.php
index 4fdf1640..5e9b1fe9 100644
--- a/classes/local/backup/restore_lifecycle_workflow.php
+++ b/classes/local/backup/restore_lifecycle_workflow.php
@@ -25,6 +25,7 @@
 use tool_lifecycle\local\entity\step_subplugin;
 use tool_lifecycle\local\entity\trigger_subplugin;
 use tool_lifecycle\local\entity\workflow;
+use tool_lifecycle\local\manager\lib_manager;
 use tool_lifecycle\local\manager\workflow_manager;
 use tool_lifecycle\local\manager\step_manager;
 use tool_lifecycle\local\manager\trigger_manager;
@@ -65,20 +66,29 @@ public function __construct($xmldata) {
      * Executes the restore process. It loads the workflow with all steps and triggers from the xml data.
      * If all data is valid, it restores the workflow with all subplugins and settings.
      * Otherwise an array with error strings is returned.
+     * @param bool $force force import, even if there are errors.
      * @return string[] Errors, which occurred during the restore process.
      * @throws \coding_exception
      * @throws \moodle_exception
      */
-    public function execute() {
+    public function execute(bool $force = false) {
         $this->reader->read();
 
         $this->load_workflow();
         // If the workflow could be loaded continue with the subplugins.
         if ($this->workflow) {
             $this->load_subplugins();
+
+            if (!$this->all_subplugins_installed()) {
+                return $this->errors;
+            }
+
             // Validate the subplugin data.
-            if (empty($this->errors) && $this->all_subplugins_installed()) {
+            $this->check_subplugin_validity();
+            if (empty($this->errors) || $force) {
                 // If all loaded data is valid, the new workflow and the steps can be stored in the database.
+                // If we force the import, we empty the errors;
+                $this->errors = [];
                 $this->persist();
             }
         }
@@ -101,7 +111,6 @@ private function load_workflow() {
         $this->workflow->timeactive = null;
         $this->workflow->timedeactive = null;
         $this->workflow->sortindex = null;
-        workflow_manager::insert_or_update($this->workflow);
     }
 
     /**
@@ -174,6 +183,41 @@ private function all_subplugins_installed() {
         return true;
     }
 
+    /**
+     * Calls the subplugins to check the consistency and validity of the step and trigger settings.
+     */
+    private function check_subplugin_validity() {
+        foreach ($this->steps as $step) {
+            $steplib = lib_manager::get_step_lib($step->subpluginname);
+            $filteredsettings = [];
+            foreach ($this->settings as $setting) {
+                if ($setting->pluginid === $step->id) {
+                    $filteredsettings[$setting->name] = $setting->value;
+                }
+            }
+            $errors = array_map(
+                    fn($x) => get_string('restore_error_in_step', 'tool_lifecycle', $step->instancename) . $x,
+                    $steplib->ensure_validity($filteredsettings)
+            );
+            $this->errors = array_merge($this->errors, $errors);
+        }
+
+        foreach ($this->trigger as $trigger) {
+            $steplib = lib_manager::get_trigger_lib($trigger->subpluginname);
+            $filteredsettings = [];
+            foreach ($this->settings as $setting) {
+                if ($setting->pluginid === $trigger->id) {
+                    $filteredsettings[$setting->name] = $setting->value;
+                }
+            }
+            $errors = array_map(
+                    fn($x) => get_string('restore_error_in_trigger', 'tool_lifecycle', $trigger->instancename) . $x,
+                    $steplib->ensure_validity($filteredsettings)
+            );
+            $this->errors = array_merge($this->errors, $errors);
+        }
+    }
+
     /**
      * Stores all loaded data in the database.
      * @throws \moodle_exception
diff --git a/classes/local/form/form_upload_workflow.php b/classes/local/form/form_upload_workflow.php
index 5ccd6aec..ee30d441 100644
--- a/classes/local/form/form_upload_workflow.php
+++ b/classes/local/form/form_upload_workflow.php
@@ -43,6 +43,12 @@ public function definition() {
 
         $mform->addElement('filepicker', 'backupfile', get_string('file'), null,
             ['accepted_types' => 'xml']);
+
+        $showforce = isset($this->_customdata['showforce']) && $this->_customdata['showforce'];
+        $mform->addElement($showforce ? 'checkbox' : 'hidden', 'force', get_string('force_import', 'tool_lifecycle'));
+        $mform->setDefault('force', 0);
+        $mform->setType('force', PARAM_BOOL);
+
         $this->add_action_buttons('true', get_string('upload'));
     }
 
diff --git a/lang/en/tool_lifecycle.php b/lang/en/tool_lifecycle.php
index c88413f3..fb99fb1a 100644
--- a/lang/en/tool_lifecycle.php
+++ b/lang/en/tool_lifecycle.php
@@ -188,6 +188,10 @@
 $string['restore_subplugins_invalid'] = 'Wrong format of the backup file. The structure of the subplugin elements is not as expected.';
 $string['restore_step_does_not_exist'] = 'The step {$a} is not installed, but is included in the backup file. Please installed it first and try again.';
 $string['restore_trigger_does_not_exist'] = 'The trigger {$a} is not installed, but is included in the backup file. Please installed it first and try again.';
+$string['restore_error_in_step'] = 'An error occurred when importing step "{$a}": ';
+$string['restore_error_in_trigger'] = 'An error occurred when importing trigger "{$a}": ';
+$string['workflow_was_not_imported'] = 'The workflow was not imported!';
+$string['force_import'] = 'Try ignoring errors and import the workflow anyway. <b>Use this at your own risk!</b>';
 
 // Events.
 $string['process_triggered_event'] = 'A process has been triggered';
diff --git a/renderer.php b/renderer.php
index f9b7eb9b..6d3db9e7 100644
--- a/renderer.php
+++ b/renderer.php
@@ -53,15 +53,11 @@ public function header($title = null) {
     /**
      * Renders the workflow upload form including errors, which occured during upload.
      * @param \tool_lifecycle\local\form\form_upload_workflow $form
-     * @param array $errors
      * @throws coding_exception
      */
-    public function render_workflow_upload_form($form, $errors = []) {
+    public function render_workflow_upload_form($form) {
         $this->header(get_string('adminsettings_edit_workflow_definition_heading', 'tool_lifecycle'));
-        foreach ($errors as $error) {
-            \core\notification::add($error, \core\notification::ERROR);
-        }
-        echo $form->render();
+        $form->display();
         $this->footer();
     }
 
diff --git a/step/lib.php b/step/lib.php
index 86c8345c..20754d9b 100644
--- a/step/lib.php
+++ b/step/lib.php
@@ -142,6 +142,16 @@ public function extend_add_instance_form_definition_after_data($mform, $settings
     public function abort_course($process) {
     }
 
+
+    /**
+     * Ensure validity of settings upon backup restoration.
+     * @param array $settings
+     * @return array List of errors with settings. If empty, the given settings are valid.
+     */
+    public function ensure_validity(array $settings) : array {
+        return [];
+    }
+
 }
 
 /**
diff --git a/tests/backup_and_restore_workflow_test.php b/tests/backup_and_restore_workflow_test.php
index 2472092b..97e3a6b9 100644
--- a/tests/backup_and_restore_workflow_test.php
+++ b/tests/backup_and_restore_workflow_test.php
@@ -28,6 +28,7 @@
 require_once(__DIR__ . '/generator/lib.php');
 require_once(__DIR__ . '/../lib.php');
 
+use mod_bigbluebuttonbn\settings;
 use tool_lifecycle\local\backup\backup_lifecycle_workflow;
 use tool_lifecycle\local\backup\restore_lifecycle_workflow;
 use tool_lifecycle\local\manager\workflow_manager;
@@ -60,6 +61,14 @@ public function setUp() : void {
         $this->resetAfterTest(true);
         $generator = $this->getDataGenerator()->get_plugin_generator('tool_lifecycle');
         $this->workflow = $generator->create_workflow(['startdatedelay', 'categories'], ['email', 'createbackup', 'deletecourse']);
+        $category = $this->getDataGenerator()->create_category();
+        foreach (trigger_manager::get_triggers_for_workflow($this->workflow->id) as $trigger) {
+            if ($trigger->subpluginname === 'categories') {
+                settings_manager::save_setting($trigger->id, settings_type::TRIGGER, 'categories',
+                        'categories', $category->id);
+            }
+        }
+
         foreach (workflow_manager::get_workflows() as $existingworkflow) {
             $this->existingworkflows[] = $existingworkflow->id;
         }
diff --git a/trigger/categories/lang/de/lifecycletrigger_categories.php b/trigger/categories/lang/de/lifecycletrigger_categories.php
index fcec1378..fb3a9e89 100644
--- a/trigger/categories/lang/de/lifecycletrigger_categories.php
+++ b/trigger/categories/lang/de/lifecycletrigger_categories.php
@@ -28,3 +28,4 @@
 $string['categories'] = 'Kategorien, für die der Workflow ausgelöst werden soll.';
 $string['categories_noselection'] = 'Bitte wählen sie mindestens eine Kategorie aus.';
 $string['exclude'] = 'Falls ausgewählt, werden gerade die Kurse der angegebenen Kategorien nicht ausgelöst.';
+$string['categories_do_not_exist'] = 'Es gibt keine Kurskategorien mit den folgenden IDs: {$a}.';
diff --git a/trigger/categories/lang/en/lifecycletrigger_categories.php b/trigger/categories/lang/en/lifecycletrigger_categories.php
index 423bd48e..d065edb7 100644
--- a/trigger/categories/lang/en/lifecycletrigger_categories.php
+++ b/trigger/categories/lang/en/lifecycletrigger_categories.php
@@ -28,3 +28,4 @@
 $string['categories'] = 'Categories, for which the workflow should be triggered';
 $string['categories_noselection'] = 'Please choose at least one category.';
 $string['exclude'] = 'If ticked, the named categories are excluded from triggering instead.';
+$string['categories_do_not_exist'] = 'There are no categories with the following ids: {$a}.';
diff --git a/trigger/categories/lib.php b/trigger/categories/lib.php
index 0ace8460..95a64610 100644
--- a/trigger/categories/lib.php
+++ b/trigger/categories/lib.php
@@ -63,7 +63,7 @@ public function check_course($course, $triggerid) {
     public function get_course_recordset_where($triggerid) {
         global $DB, $CFG;
         $categories = settings_manager::get_settings($triggerid, settings_type::TRIGGER)['categories'];
-        $exclude = settings_manager::get_settings($triggerid, settings_type::TRIGGER)['exclude'] && true;
+        $exclude = settings_manager::get_settings($triggerid, settings_type::TRIGGER)['exclude'];
 
         $categories = explode(',', $categories);
         // Use core_course_category for moodle 3.6 and higher.
@@ -75,17 +75,17 @@ public function get_course_recordset_where($triggerid) {
         }
         $allcategories = [];
         foreach ($categories as $category) {
-            array_push($allcategories , $category);
+            array_push($allcategories, $category);
+            if (!isset($categoryobjects[$category]) || !$categoryobjects[$category]) {
+                continue;
+            }
             $children = $categoryobjects[$category]->get_all_children_ids();
-            $allcategories  = array_merge($allcategories , $children);
+            $allcategories = array_merge($allcategories, $children);
         }
 
-        list($insql, $inparams) = $DB->get_in_or_equal($allcategories, SQL_PARAMS_NAMED);
+        list($insql, $inparams) = $DB->get_in_or_equal($allcategories, SQL_PARAMS_NAMED, 'param', !$exclude);
 
         $where = "{course}.category {$insql}";
-        if ($exclude) {
-            $where = "NOT " . $where;
-        }
 
         return [$where, $inparams];
     }
@@ -131,4 +131,25 @@ public function extend_add_instance_form_definition($mform) {
         $mform->setType('exclude', PARAM_BOOL);
     }
 
+    /**
+     * Ensure validity of settings upon backup restoration.
+     * @param array $settings
+     * @return array List of errors with settings. If empty, the given settings are valid.
+     */
+    public function ensure_validity(array $settings): array {
+        $missingcategories = [];
+        $categories = explode(',', $settings['categories']);
+        $categoryobjects = \core_course_category::get_many($categories);
+        foreach ($categories as $category) {
+            if (!isset($categoryobjects[$category]) || !$categoryobjects[$category]) {
+                $missingcategories[] = $category;
+            }
+        }
+        if ($missingcategories) {
+            return [get_string('categories_do_not_exist', 'lifecycletrigger_categories', join(', ', $missingcategories))];
+        } else {
+            return [];
+        }
+    }
+
 }
diff --git a/trigger/lib.php b/trigger/lib.php
index 312c967c..c597c392 100644
--- a/trigger/lib.php
+++ b/trigger/lib.php
@@ -115,6 +115,15 @@ public function get_status_message() {
         return get_string("workflow_started", "tool_lifecycle");
     }
 
+    /**
+     * Ensure validity of settings upon backup restoration.
+     * @param array $settings
+     * @return array List of errors with settings. If empty, the given settings are valid.
+     */
+    public function ensure_validity(array $settings) : array {
+        return [];
+    }
+
 }
 
 /**
diff --git a/uploadworkflow.php b/uploadworkflow.php
index 06161e1a..351adebb 100644
--- a/uploadworkflow.php
+++ b/uploadworkflow.php
@@ -22,6 +22,7 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+use core\notification;
 use tool_lifecycle\local\backup\restore_lifecycle_workflow;
 use tool_lifecycle\local\form\form_upload_workflow;
 use tool_lifecycle\permission_and_navigation;
@@ -51,11 +52,18 @@
 if ($data = $form->get_data()) {
     $xmldata = $form->get_file_content('backupfile');
     $restore = new restore_lifecycle_workflow($xmldata);
-    $errors = $restore->execute();
+    $force = $data->force ?? false;
+    $errors = $restore->execute($force);
     if (count($errors) != 0) {
+        notification::add(get_string('workflow_was_not_imported', 'tool_lifecycle'), notification::ERROR);
+        foreach (array_unique($errors) as $error) {
+            notification::add($error, notification::ERROR);
+        }
+        $form = new form_upload_workflow(null, ['showforce' => true]);
+
         /** @var \tool_lifecycle_renderer $renderer */
         $renderer = $PAGE->get_renderer('tool_lifecycle');
-        $renderer->render_workflow_upload_form($form, $errors);
+        $renderer->render_workflow_upload_form($form);
         die();
     } else {
         // Redirect to workflow page.