diff --git a/src/include/api/class-wc-retailcrm-client-v5.php b/src/include/api/class-wc-retailcrm-client-v5.php
index 7ae24ff..3ec37cd 100644
--- a/src/include/api/class-wc-retailcrm-client-v5.php
+++ b/src/include/api/class-wc-retailcrm-client-v5.php
@@ -893,7 +893,7 @@ class WC_Retailcrm_Client_V5
             );
         }
             
-        if (empty($entity) || !in_array($entity, ['customer', 'order', 'customer_corporate', 'company'])) {
+        if (empty($entity) || !in_array($entity, array('customer', 'order', 'customer_corporate', 'company'))) {
             throw new \InvalidArgumentException(
                 sprintf(
                     'Parameter `entity` must contain a data & value must be %s',
diff --git a/src/include/api/class-wc-retailcrm-proxy.php b/src/include/api/class-wc-retailcrm-proxy.php
index 9ff3112..9256055 100644
--- a/src/include/api/class-wc-retailcrm-proxy.php
+++ b/src/include/api/class-wc-retailcrm-proxy.php
@@ -70,12 +70,14 @@ if ( ! class_exists( 'WC_Retailcrm_Proxy' ) ) :
          */
         private function methodsWithoutDebugResponse()
         {
-            return array_map(
-                function ($val) {
-                    return get_class($this->retailcrm) . '::' . $val;
-                },
-                array('statusesList', 'paymentTypesList', 'deliveryTypesList', 'orderMethodsList')
-            );
+            $methodsList = array('statusesList', 'paymentTypesList', 'deliveryTypesList', 'orderMethodsList');
+
+            foreach ($methodsList as $key => $method) {
+                $method = get_class($this->retailcrm) . '::' . $method;
+                $methodsList[$key] = $method;
+            }
+
+            return $methodsList;
         }
 
         public function __call($method, $arguments)
@@ -87,13 +89,13 @@ if ( ! class_exists( 'WC_Retailcrm_Proxy' ) ) :
             try {
                 WC_Retailcrm_Logger::debug(
                     $called,
-                    empty($arguments) ? '[no params]' : print_r($arguments, true)
+                    array(empty($arguments) ? '[no params]' : print_r($arguments, true))
                 );
                 /** @var \WC_Retailcrm_Response $response */
                 $response = call_user_func_array(array($this->retailcrm, $method), $arguments);
 
                 if (is_string($response)) {
-                    WC_Retailcrm_Logger::debug($called, $response);
+                    WC_Retailcrm_Logger::debug($called, array($response));
                     return $response;
                 }
 
@@ -105,9 +107,9 @@ if ( ! class_exists( 'WC_Retailcrm_Proxy' ) ) :
                             $called,
                             $this->methodsWithoutDebugResponse()
                         )) {
-                            WC_Retailcrm_Logger::debug($called, '[request was successful, but response is omitted]');
+                            WC_Retailcrm_Logger::debug($called, array('[request was successful, but response is omitted]'));
                         } else {
-                            WC_Retailcrm_Logger::debug($called, $response->getRawResponse());
+                            WC_Retailcrm_Logger::debug($called, array($response->getRawResponse()));
                         }
                     }
 
@@ -123,22 +125,22 @@ if ( ! class_exists( 'WC_Retailcrm_Proxy' ) ) :
                         $result .= self::reduceErrors($response['errors']);
                     }
 
-                    WC_Retailcrm_Logger::debug($called, $response->getErrorString());
-                    WC_Retailcrm_Logger::debug($called, $response->getRawResponse());
+                    WC_Retailcrm_Logger::debug($called, array($response->getErrorString()));
+                    WC_Retailcrm_Logger::debug($called, array($response->getRawResponse()));
                 }
 
                 WC_Retailcrm_Logger::add(sprintf("[%s] %s", $called, $result));
             } catch (WC_Retailcrm_Exception_Curl $exception) {
-                WC_Retailcrm_Logger::debug(get_class($this->retailcrm).'::'.$called, $exception->getMessage());
-                WC_Retailcrm_Logger::debug('', $exception->getTraceAsString());
+                WC_Retailcrm_Logger::debug(get_class($this->retailcrm).'::'.$called, array($exception->getMessage()));
+                WC_Retailcrm_Logger::debug('', array($exception->getTraceAsString()));
                 WC_Retailcrm_Logger::add(sprintf("[%s] %s - %s", $called, $exception->getMessage(), $result));
             } catch (WC_Retailcrm_Exception_Json $exception) {
-                WC_Retailcrm_Logger::debug(get_class($this->retailcrm).'::'.$called, $exception->getMessage());
-                WC_Retailcrm_Logger::debug('', $exception->getTraceAsString());
+                WC_Retailcrm_Logger::debug(get_class($this->retailcrm).'::'.$called, array($exception->getMessage()));
+                WC_Retailcrm_Logger::debug('', array($exception->getTraceAsString()));
                 WC_Retailcrm_Logger::add(sprintf("[%s] %s - %s", $called, $exception->getMessage(), $result));
             } catch (InvalidArgumentException $exception) {
-                WC_Retailcrm_Logger::debug(get_class($this->retailcrm).'::'.$called, $exception->getMessage());
-                WC_Retailcrm_Logger::debug('', $exception->getTraceAsString());
+                WC_Retailcrm_Logger::debug(get_class($this->retailcrm).'::'.$called, array($exception->getMessage()));
+                WC_Retailcrm_Logger::debug('', array($exception->getTraceAsString()));
                 WC_Retailcrm_Logger::add(sprintf("[%s] %s - %s", $called, $exception->getMessage(), $result));
             }
 
diff --git a/src/include/class-wc-retailcrm-history.php b/src/include/class-wc-retailcrm-history.php
index c127c2c..6de59a5 100644
--- a/src/include/class-wc-retailcrm-history.php
+++ b/src/include/class-wc-retailcrm-history.php
@@ -157,10 +157,14 @@ if ( ! class_exists( 'WC_Retailcrm_History' ) ) :
                 $customers = WC_Retailcrm_History_Assembler::assemblyCustomer($history);
                 WC_Retailcrm_Plugin::$history_run = true;
 <<<<<<< HEAD
+<<<<<<< HEAD
 >>>>>>> WIP: Change client in the order (not ready at this point; also tests should fail)
 =======
                 WC_Retailcrm_Logger::debug(__METHOD__, 'Assembled customers history:', $customers);
 >>>>>>> WIP: Logic for company replacement via component (which was surprisingly easy to implement)
+=======
+                WC_Retailcrm_Logger::debug(__METHOD__, array('Assembled customers history:', $customers));
+>>>>>>> Compatibility fixes for php 5.3
 
                 foreach ($customers as $crmCustomer) {
                     if (!isset($crmCustomer['externalId'])) {
@@ -187,7 +191,7 @@ if ( ! class_exists( 'WC_Retailcrm_History' ) ) :
                             $wcCustomer->save();
                         }
 
-                        WC_Retailcrm_Logger::debug(__METHOD__, 'Updated WC_Customer:', $wcCustomer);
+                        WC_Retailcrm_Logger::debug(__METHOD__, array('Updated WC_Customer:', $wcCustomer));
                     } catch (\Exception $exception) {
                         WC_Retailcrm_Logger::error(sprintf(
                             'Error while trying to process history: %s',
@@ -244,7 +248,7 @@ if ( ! class_exists( 'WC_Retailcrm_History' ) ) :
             if (!empty($history)) {
                 $last_change = end($history);
                 $historyAssembly = WC_Retailcrm_History_Assembler::assemblyOrder($history);
-                WC_Retailcrm_Logger::debug(__METHOD__, 'Assembled orders history:', $historyAssembly);
+                WC_Retailcrm_Logger::debug(__METHOD__, array('Assembled orders history:', $historyAssembly));
                 WC_Retailcrm_Plugin::$history_run = true;
 
                 foreach ($historyAssembly as $orderHistory) {
@@ -922,8 +926,10 @@ if ( ! class_exists( 'WC_Retailcrm_History' ) ) :
 
             WC_Retailcrm_Logger::debug(
                 __METHOD__,
-                'processing order',
-                $order
+                array(
+                    'processing order',
+                    $order
+                )
             );
 
             if (isset($order['customer'])) {
diff --git a/src/include/components/class-wc-retailcrm-customer-switcher.php b/src/include/components/class-wc-retailcrm-customer-switcher.php
index 0cd8500..ab7692c 100644
--- a/src/include/components/class-wc-retailcrm-customer-switcher.php
+++ b/src/include/components/class-wc-retailcrm-customer-switcher.php
@@ -36,34 +36,42 @@ class WC_Retailcrm_Customer_Switcher implements WC_Retailcrm_Builder_Interface
     {
         $this->data->validate();
 
-        WC_Retailcrm_Logger::debug(__METHOD__, 'state', $this->data);
+        WC_Retailcrm_Logger::debug(__METHOD__, array('state', $this->data));
 
-        if (!empty($this->data->getNewCustomer())) {
+        $newCustomer = $this->data->getNewCustomer();
+        $newContact = $this->data->getNewContact();
+        $newCompany = $this->data->getNewCompanyName();
+
+        if (!empty($newCustomer)) {
             WC_Retailcrm_Logger::debug(
                 __METHOD__,
-                'Changing to individual customer for order',
-                $this->data->getWcOrder()->get_id()
+                array(
+                    'Changing to individual customer for order',
+                    $this->data->getWcOrder()->get_id()
+                )
             );
-            $this->processChangeToRegular($this->data->getWcOrder(), $this->data->getNewCustomer());
+            $this->processChangeToRegular($this->data->getWcOrder(), $newCustomer);
         } else {
-            if (!empty($this->data->getNewContact())) {
+            if (!empty($newContact)) {
                 WC_Retailcrm_Logger::debug(
                     __METHOD__,
-                    'Changing to contact person customer for order',
-                    $this->data->getWcOrder()->get_id()
+                    array(
+                        'Changing to contact person customer for order',
+                        $this->data->getWcOrder()->get_id()
+                    )
                 );
-                $this->processChangeToRegular($this->data->getWcOrder(), $this->data->getNewContact());
+                $this->processChangeToRegular($this->data->getWcOrder(), $newContact);
             }
 
-            if (!empty($this->data->getNewCompanyName())) {
+            if (!empty($newCompany)) {
                 WC_Retailcrm_Logger::debug(
                     __METHOD__,
-                    sprintf(
+                    array(sprintf(
                         'Replacing old order id=`%d` company `%s` with new company `%s`',
                         $this->data->getWcOrder()->get_id(),
                         $this->data->getWcOrder()->get_billing_company(),
-                        $this->data->getNewCompanyName()
-                    )
+                        $newCompany
+                    ))
                 );
                 $this->processCompanyChange();
             }
@@ -86,10 +94,12 @@ class WC_Retailcrm_Customer_Switcher implements WC_Retailcrm_Builder_Interface
 
         WC_Retailcrm_Logger::debug(
             __METHOD__,
-            'Switching in order',
-            $wcOrder->get_id(),
-            'to',
-            $newCustomer
+            array(
+                'Switching in order',
+                $wcOrder->get_id(),
+                'to',
+                $newCustomer
+            )
         );
 
         if (isset($newCustomer['externalId'])) {
@@ -99,18 +109,22 @@ class WC_Retailcrm_Customer_Switcher implements WC_Retailcrm_Builder_Interface
                 $wcOrder->set_customer_id($wcCustomer->get_id());
                 WC_Retailcrm_Logger::debug(
                     __METHOD__,
-                    'Set customer to',
-                    $wcCustomer->get_id(),
-                    'in order',
-                    $wcOrder->get_id()
+                    array(
+                        'Set customer to',
+                        $wcCustomer->get_id(),
+                        'in order',
+                        $wcOrder->get_id()
+                    )
                 );
             }
         } else {
             $wcOrder->set_customer_id(0);
             WC_Retailcrm_Logger::debug(
                 __METHOD__,
-                'Set customer to 0 (guest) in order',
-                $wcOrder->get_id()
+                array(
+                    'Set customer to 0 (guest) in order',
+                    $wcOrder->get_id()
+                )
             );
         }
 
@@ -148,8 +162,10 @@ class WC_Retailcrm_Customer_Switcher implements WC_Retailcrm_Builder_Interface
             }
         }
 
-        if (!empty(self::singleCustomerPhone($newCustomer))) {
-            $wcOrder->set_billing_phone(self::singleCustomerPhone($newCustomer));
+        $customerPhone = self::singleCustomerPhone($newCustomer);
+
+        if (!empty($customerPhone)) {
+            $wcOrder->set_billing_phone($customerPhone);
         }
 
         $wcOrder->set_billing_company('');
diff --git a/src/include/components/class-wc-retailcrm-logger.php b/src/include/components/class-wc-retailcrm-logger.php
index 319ecb4..46d1f22 100644
--- a/src/include/components/class-wc-retailcrm-logger.php
+++ b/src/include/components/class-wc-retailcrm-logger.php
@@ -81,7 +81,7 @@ if (!class_exists('WC_Retailcrm_Logger') && class_exists('WC_Log_Levels')):
          * @param string $method
          * @param array  $messages
          */
-        public static function debug($method, ...$messages)
+        public static function debug($method, $messages)
         {
             if (retailcrm_is_debug()) {
                 if (!empty($method) && !empty($messages)) {
diff --git a/src/include/customer/woocommerce/class-wc-retailcrm-wc-customer-builder.php b/src/include/customer/woocommerce/class-wc-retailcrm-wc-customer-builder.php
index 2ad5dc6..afbd792 100644
--- a/src/include/customer/woocommerce/class-wc-retailcrm-wc-customer-builder.php
+++ b/src/include/customer/woocommerce/class-wc-retailcrm-wc-customer-builder.php
@@ -145,7 +145,7 @@ class WC_Retailcrm_WC_Customer_Builder extends WC_Retailcrm_Abstract_Builder
     public function build()
     {
         $this->checkBuilderValidity();
-        WC_Retailcrm_Logger::debug(__METHOD__, 'Building WC_Customer from data:', $this->data);
+        WC_Retailcrm_Logger::debug(__METHOD__, array('Building WC_Customer from data:', $this->data));
         $this->customer->set_first_name($this->dataValue('firstName', $this->customer->get_first_name()));
         $this->customer->set_last_name($this->dataValue('lastName', $this->customer->get_last_name()));
         $this->customer->set_billing_email($this->dataValue('email', $this->customer->get_billing_email()));
@@ -159,9 +159,9 @@ class WC_Retailcrm_WC_Customer_Builder extends WC_Retailcrm_Abstract_Builder
             }
         }
 
-        if (!empty($this->dataValue('address'))) {
-            $address = $this->dataValue('address');
+        $address = $this->dataValue('address');
 
+        if (!empty($address)) {
             $this->customer->set_billing_state(self::arrayValue(
                 $address,
                 'region',
diff --git a/src/include/models/class-wc-retailcrm-customer-switcher-result.php b/src/include/models/class-wc-retailcrm-customer-switcher-result.php
index 0664db5..d6b193c 100644
--- a/src/include/models/class-wc-retailcrm-customer-switcher-result.php
+++ b/src/include/models/class-wc-retailcrm-customer-switcher-result.php
@@ -57,9 +57,11 @@ class WC_Retailcrm_Customer_Switcher_Result
     {
         WC_Retailcrm_Logger::debug(
             __METHOD__,
-            'Saving customer and order:',
-            $this->wcCustomer,
-            $this->wcOrder
+            array(
+                'Saving customer and order:',
+                $this->wcCustomer,
+                $this->wcOrder
+            )
         );
 
         if (!empty($this->wcCustomer)) {
diff --git a/src/include/models/class-wc-retailcrm-customer-switcher-state.php b/src/include/models/class-wc-retailcrm-customer-switcher-state.php
index 256016b..d75412a 100644
--- a/src/include/models/class-wc-retailcrm-customer-switcher-state.php
+++ b/src/include/models/class-wc-retailcrm-customer-switcher-state.php
@@ -116,20 +116,22 @@ class WC_Retailcrm_Customer_Switcher_State
      */
     public function validate()
     {
-        if (empty($this->getWcOrder())) {
+        if (empty($this->wcOrder)) {
             throw new \InvalidArgumentException('Empty WC_Order.');
         }
 
-        if (empty($this->getNewCustomer()) && empty($this->getNewContact()) && empty($this->getNewCompanyName())) {
+        if (empty($this->newCustomer) && empty($this->newContact) && empty($this->newCompanyName)) {
             throw new \InvalidArgumentException('New customer, new contact and new company is empty.');
         }
 
-        if (!empty($this->getNewCustomer()) && !empty($this->getNewContact())) {
+        if (!empty($this->newCustomer) && !empty($this->newContact)) {
             WC_Retailcrm_Logger::debug(
                 __METHOD__,
-                'State data (customer and contact):' . PHP_EOL,
-                $this->getNewCustomer(),
-                $this->getNewContact()
+                array(
+                    'State data (customer and contact):' . PHP_EOL,
+                    $this->getNewCustomer(),
+                    $this->getNewContact()
+                )
             );
             throw new \InvalidArgumentException(
                 'Too much data in state - cannot determine which customer should be used.'