diff --git a/lib/errors.rb b/lib/errors.rb
index 6670dc4..68180c8 100644
--- a/lib/errors.rb
+++ b/lib/errors.rb
@@ -27,5 +27,8 @@ def initialize(message, payment_id, txid)
         @payment_id = payment_id
         @txid = txid
     end
+
+    class WalletPrivateSeedNotFoundError < StandardError
+    end
   end
 end
\ No newline at end of file
diff --git a/lib/pi_network.rb b/lib/pi_network.rb
index 398d732..a4c6e39 100644
--- a/lib/pi_network.rb
+++ b/lib/pi_network.rb
@@ -12,10 +12,12 @@ class PiNetwork
   attr_reader :base_url
   attr_reader :from_address
 
-  def initialize(api_key, wallet_private_key, options = {})
-    validate_private_seed_format!(wallet_private_key)
+  def initialize(api_key, options = {})
+    wallet_private_seed = options[:wallet_private_seed]
+    validate_private_seed_format!(wallet_private_seed) if wallet_private_seed.present?
+
     @api_key = api_key
-    @account = load_account(wallet_private_key)
+    @account = load_account(wallet_private_seed)
     @base_url = options[:base_url] || "https://api.minepi.com"
 
     @open_payments = {}
@@ -57,6 +59,10 @@ def create_payment(payment_data)
   end
 
   def submit_payment(payment_id)
+    raise Errors::WalletPrivateSeedNotFoundError.new(
+      "You need to initialize the SDK with wallet_private_seed to call this method."
+    ) if self.account.nil?
+
     payment = @open_payments[payment_id]
 
     if payment.nil? || payment["identifier"] != payment_id
diff --git a/pinetwork.gemspec b/pinetwork.gemspec
index 221d1c1..9b305e4 100644
--- a/pinetwork.gemspec
+++ b/pinetwork.gemspec
@@ -1,6 +1,6 @@
 Gem::Specification.new do |s|
   s.name        = "pinetwork"
-  s.version     = "0.1.2"
+  s.version     = "0.2.0"
   s.summary     = "Pi Network Ruby"
   s.description = "Pi Network backend library for Ruby-based webservers."
   s.authors     = ["Pi Core Team"]