diff --git a/README.md b/README.md
index 0478fa8..ab013f7 100644
--- a/README.md
+++ b/README.md
@@ -28,6 +28,8 @@ $ gem install cloud_payments
 
 ### Configuration
 
+#### Common usage. Global configuration:
+
 ```ruby
 CloudPayments.configure do |c|
   c.host = 'http://localhost:3000'    # By default, it is https://api.cloudpayments.ru
@@ -39,6 +41,18 @@ CloudPayments.configure do |c|
 end
 ```
 
+use can use CloudPayments.client and other resources with these global config.
+
+#### Local configuration:
+
+```ruby
+config = CloudPayments::Config.configure do |c|
+  c.host = 'http://localhost:3000'    # By default, it is https://api.cloudpayments.ru
+  c.public_key = ''
+  c.secret_key = ''
+end
+```
+
 ### Test method
 
 ```ruby
@@ -48,6 +62,8 @@ CloudPayments.client.ping
 
 ### Cryptogram-based payments
 
+#### With global configuration:
+
 ```ruby
 transaction = CloudPayments.client.payments.cards.charge(
   amount: 120,
@@ -95,6 +111,13 @@ transaction.token
 # => "a4e67841-abb0-42de-a364-d1d8f9f4b3c0"
 ```
 
+#### With local configuration:
+
+```ruby
+client = CloudPayment::Client.new(config)
+client.payments.cards.charge(...)
+```
+
 ## Webhooks
 
 ```ruby
diff --git a/lib/cloud_payments/client.rb b/lib/cloud_payments/client.rb
index f635caa..089edf5 100644
--- a/lib/cloud_payments/client.rb
+++ b/lib/cloud_payments/client.rb
@@ -10,8 +10,8 @@ class Client
 
     attr_reader :config, :connection
 
-    def initialize
-      @config = CloudPayments.config
+    def initialize(config = nil)
+      @config = config || CloudPayments.config
       @connection = build_connection
     end
 
diff --git a/lib/cloud_payments/client/serializer/base.rb b/lib/cloud_payments/client/serializer/base.rb
index c977625..4a7cb96 100644
--- a/lib/cloud_payments/client/serializer/base.rb
+++ b/lib/cloud_payments/client/serializer/base.rb
@@ -40,7 +40,7 @@ def convert_keys_from_api(attributes)
 
         def convert_keys_to_api(attributes)
           attributes.each_with_object({}) do |(key, value), result|
-            value = convert_keys_to_api(value) if value.is_a?(Hash)
+            value = convert_keys_to_api(value) if value.is_a?(Hash) && (key.to_s != 'json_data')
 
             key = key.to_s.gsub(/^[a-z\d]*/){ $&.capitalize }
             key.gsub!(/(?:_|(\/))([a-z\d]*)/i){ "#{$1}#{$2.capitalize}" }
diff --git a/lib/cloud_payments/config.rb b/lib/cloud_payments/config.rb
index c453df3..286f51a 100644
--- a/lib/cloud_payments/config.rb
+++ b/lib/cloud_payments/config.rb
@@ -12,6 +12,12 @@ class Config
       logger
     }
 
+    def self.configure
+      config = new
+      yield config
+      config
+    end
+
     def initialize
       @log = false
       @serializer = Client::Serializer::MultiJson.new(self)
diff --git a/lib/cloud_payments/namespaces/base.rb b/lib/cloud_payments/namespaces/base.rb
index f16e974..0e0fc4a 100644
--- a/lib/cloud_payments/namespaces/base.rb
+++ b/lib/cloud_payments/namespaces/base.rb
@@ -36,7 +36,9 @@ def raise_gateway_error(body)
       end
 
       def raise_reasoned_gateway_error(body)
-        fail Client::GATEWAY_ERRORS[body[:model][:reason_code]].new(body) if reason_present?(body)
+        return unless reason_present?(body)
+        error_class = Client::GATEWAY_ERRORS[body[:model][:reason_code]]
+        fail error_class.new(body) if error_class
       end
 
       def raise_raw_gateway_error(body)
diff --git a/lib/cloud_payments/webhooks.rb b/lib/cloud_payments/webhooks.rb
index d5ef61c..b27df4a 100644
--- a/lib/cloud_payments/webhooks.rb
+++ b/lib/cloud_payments/webhooks.rb
@@ -8,8 +8,8 @@ class HMACError < StandardError; end
 
     attr_reader :config
 
-    def initialize
-      @config = CloudPayments.config
+    def initialize(config = nil)
+      @config = config || CloudPayments.config
       @digest = OpenSSL::Digest.new('sha256')
       @serializer = Client::Serializer::Base.new(config)
     end