diff --git a/classes/category/options.php b/classes/category/options.php
index e989eb0f..630e9ea2 100644
--- a/classes/category/options.php
+++ b/classes/category/options.php
@@ -108,12 +108,13 @@ public function get_parents_options() {
      * @return array[string]
      */
     public static function get_all_categories_options() {
-        $catoptions = [0 => get_string('any')];
+        $catoptions = [];
         $allcats = \core_course_category::get_all();
         foreach ($allcats as $catid => $cat) {
             $catoptions[$catid] = $cat->get_nested_name(false);
         }
         asort($catoptions, SORT_STRING | SORT_FLAG_CASE);
+        $catoptions = [0 => get_string('any')] + $catoptions;
         return $catoptions;
     }
 
diff --git a/classes/privacy/provider.php b/classes/privacy/provider.php
index 030eaadc..8e169bea 100644
--- a/classes/privacy/provider.php
+++ b/classes/privacy/provider.php
@@ -46,7 +46,7 @@ class provider implements
      * @param collection $collection The initialized collection to add items to.
      * @return collection A listing of user data stored through this system.
      */
-    public static function get_metadata(collection $collection) :collection {
+    public static function get_metadata(collection $collection): collection {
         $collection->add_database_table('enrol_wallet_items', [
             'userid'     => "privacy:metadata:enrol_wallet_items:userid",
             'cost'       => "privacy:metadata:enrol_wallet_items:cost",
diff --git a/classes/util/balance.php b/classes/util/balance.php
index 7b093875..d80ffcc5 100644
--- a/classes/util/balance.php
+++ b/classes/util/balance.php
@@ -181,7 +181,7 @@ protected function set_main_balance() {
      * from the transaction table.
      * @return float
      */
-    private function get_nonrefund_from_transactions():float {
+    private function get_nonrefund_from_transactions(): float {
         global $DB;
         $balance = $this->get_main_balance();
         $record = $DB->get_records('enrol_wallet_transactions', ['userid' => $this->userid], 'id DESC', 'norefund', 0, 1);
diff --git a/classes/util/cm.php b/classes/util/cm.php
index 8715bf9c..4846fee1 100644
--- a/classes/util/cm.php
+++ b/classes/util/cm.php
@@ -98,7 +98,7 @@ public function __construct($cmid, $userid = 0) {
      * Set all available costs for this cm, considering multiple conditions may be applied.
      * @param \stdClass $conditions the availability tree.
      */
-    private function set_costs ($conditions) {
+    private function set_costs($conditions) {
         foreach ($conditions->c as $child) {
             if (!empty($child->c) && !empty($child->op)) {
                 $this->set_costs($child);
diff --git a/styles.css b/styles.css
index fda76d94..d3e38531 100644
--- a/styles.css
+++ b/styles.css
@@ -133,7 +133,7 @@
         font-size: 0.8em;
     }
 }
-  
+
 .enrol_wallet_topup .accordion .accordion__title {
     display: block;
     font-size: 1.1rem;
diff --git a/tests/coupons_test.php b/tests/coupons_test.php
index b1a2c6f1..cba96b17 100644
--- a/tests/coupons_test.php
+++ b/tests/coupons_test.php
@@ -78,7 +78,7 @@ class coupons_test extends \advanced_testcase {
      * Test if a certain type of coupons are enabled
      * @covers ::is_enabled_type
      */
-    public function test_is_enabled_type():void {
+    public function test_is_enabled_type(): void {
         $this->setUser($this->u2);
         $coupons = new coupons('fixed1');
         $this->assertFalse($coupons->is_enabled_type());
@@ -119,7 +119,7 @@ public function test_is_enabled_type():void {
      * Test if coupons are enabled in this site.
      * @covers ::is_enabled()
      */
-    public function test_is_enabled():void {
+    public function test_is_enabled(): void {
         $this->assertFalse(coupons::is_enabled());
         $this->set_config(coupons::DISCOUNT);
         $this->assertTrue(coupons::is_enabled());
@@ -138,7 +138,7 @@ public function test_is_enabled():void {
      * Test validation for fixed coupons
      * @covers ::validate_coupon()
      */
-    public function test_validate_fixed_coupon():void {
+    public function test_validate_fixed_coupon(): void {
         $this->set_config(coupons::ALL);
         // Not logged in.
         $coupons = new coupons('fixed1');
@@ -212,7 +212,7 @@ public function test_validate_fixed_coupon():void {
      * Test validation for enrol coupons
      * @covers ::validate_coupon
      */
-    public function test_validate_enrol_coupon():void {
+    public function test_validate_enrol_coupon(): void {
         $this->setUser($this->u1);
         $this->set_config([coupons::ENROL]);
         $coupons = new coupons('enrol1');
@@ -329,7 +329,7 @@ public function test_validate_enrol_coupon():void {
      * Validation for discount coupons.
      * @covers ::validate_coupon()
      */
-    public function test_validate_discount_coupon():void {
+    public function test_validate_discount_coupon(): void {
         $this->set_config(coupons::DISCOUNT);
         $coupons = new coupons('percent1');
         $this->assertNotTrue($coupons->validate_coupon(coupons::AREA_ENROL, $this->inst1->id));
@@ -437,7 +437,7 @@ public function test_validate_discount_coupon():void {
      * Validate category coupons
      * @covers ::validate_coupons()
      */
-    public function test_validate_category_coupon():void {
+    public function test_validate_category_coupon(): void {
         $this->set_config(coupons::CATEGORY);
         // Not logged in.
         $coupons = new coupons('category1');
@@ -506,7 +506,7 @@ public function test_validate_category_coupon():void {
      * Test applying fixed coupon
      * @covers ::apply_coupon()
      */
-    public function test_apply_fixed_coupon():void {
+    public function test_apply_fixed_coupon(): void {
         $this->set_config(coupons::FIXED);
         $coupons = new coupons('fixed1', $this->u1->id);
         $coupons->apply_coupon();
@@ -576,7 +576,7 @@ public function test_apply_fixed_coupon():void {
      * Test applying category coupon
      * @covers ::apply_coupon()
      */
-    public function test_apply_category_coupon():void {
+    public function test_apply_category_coupon(): void {
         $this->set_config(coupons::CATEGORY);
 
         $this->setUser($this->u1);
@@ -616,7 +616,7 @@ public function test_apply_category_coupon():void {
      * Test applying enrol coupons
      * @covers ::apply_coupon
      */
-    public function test_apply_enrol_coupon():void {
+    public function test_apply_enrol_coupon(): void {
         $this->set_config(coupons::ENROL);
         $this->setUser($this->u1);
         $coupons = new coupons('enrol1');
@@ -647,7 +647,7 @@ public function test_apply_enrol_coupon():void {
      * Generate a number of coupons of different data, types and restrictions
      * to be tested.
      */
-    protected function setUp() :void {
+    protected function setUp(): void {
         parent::setUp();
         global $DB, $CFG;
         require_once($CFG->dirroot."/enrol/wallet/locallib.php");
@@ -945,7 +945,7 @@ protected function setUp() :void {
      * We will use this frequently, so we can shorten the arguments.
      * @param int|array $value
      */
-    private function set_config($value) {
+    private function set_config($value): void {
         if (is_array($value)) {
             $value = implode(',', $value);
         }
diff --git a/tests/util/balance_op_test.php b/tests/util/balance_op_test.php
index 4a73dd92..c63beb13 100644
--- a/tests/util/balance_op_test.php
+++ b/tests/util/balance_op_test.php
@@ -188,7 +188,7 @@ public function test_conditional_discount_charging(): void {
      * @covers ::credit
      * @return void
      */
-    public function test_credit():void {
+    public function test_credit(): void {
         global $DB;
         $this->resetAfterTest();
         $gen = $this->getDataGenerator();
@@ -377,7 +377,7 @@ public function test_credit():void {
      * @covers ::credit
      * @return void
      */
-    public function test_credit_nocat():void {
+    public function test_credit_nocat(): void {
         global $DB;
         $this->resetAfterTest();
         $gen = $this->getDataGenerator();
@@ -506,7 +506,7 @@ public function test_credit_nocat():void {
      * @covers ::debit
      * @return void
      */
-    public function test_debit():void {
+    public function test_debit(): void {
         global $DB;
         $this->resetAfterTest();
         $gen = $this->getDataGenerator();
@@ -640,7 +640,7 @@ public function test_debit():void {
      * @covers ::debit
      * @return void
      */
-    public function test_debit_nocat():void {
+    public function test_debit_nocat(): void {
         global $DB;
         $this->resetAfterTest();
         set_config('catbalance', 0, 'enrol_wallet');
@@ -802,7 +802,7 @@ public function test_debit_nocat():void {
      * @covers ::get_total_free
      * @return void
      */
-    public function test_free_balance():void {
+    public function test_free_balance(): void {
         global $DB;
         $this->resetAfterTest();
         $gen = $this->getDataGenerator();
@@ -940,7 +940,7 @@ public function test_free_balance():void {
      * Test transferring balance to another user.
      * @covers ::transfer_to_other()
      */
-    public function test_transfer_to_other():void {
+    public function test_transfer_to_other(): void {
         $this->resetAfterTest();
         $gen = $this->getDataGenerator();
         $user1 = $gen->create_user();
@@ -1029,7 +1029,7 @@ public function test_transfer_to_other():void {
      * Used to reset the balance of a user to zero.
      * @param int $userid
      */
-    private function reset_balance($userid):void {
+    private function reset_balance($userid): void {
         $op = new balance_op($userid);
         $op->debit($op->get_valid_balance(), $op::OTHER);
         $details = $op->get_balance_details();
diff --git a/tests/util/instance_test.php b/tests/util/instance_test.php
index 71e79e03..60ab06c2 100644
--- a/tests/util/instance_test.php
+++ b/tests/util/instance_test.php
@@ -142,7 +142,7 @@ public function test_get_cost_after_discount(): void {
      * Testing discounts after first and second repurchase
      * @covers ::get_cost_after_discount
      */
-    public function test_repurchase_discount_and_function():void {
+    public function test_repurchase_discount_and_function(): void {
         global $DB;
         $this->resetAfterTest();
         $wallet = new enrol_wallet_plugin;