diff --git a/database/migrations/create_payments_table.php.stub b/database/migrations/create_payments_table.php.stub
index 2fc008f..ed94215 100644
--- a/database/migrations/create_payments_table.php.stub
+++ b/database/migrations/create_payments_table.php.stub
@@ -30,9 +30,9 @@ class CreatePaymentsTable extends Migration
             $table->string('description');
 
             $table->string('state')->default(PaymentState::defaultValue());
-            $table->json('parameters');
+            $table->text('parameters');
 
-            $table->timestamp('completed_at');
+            $table->dateTime('completed_at')->nullable();
             $table->timestamps();
             $table->softDeletes();
         });
diff --git a/src/Payments/Payment.php b/src/Payments/Payment.php
index 6c283a8..4091e48 100644
--- a/src/Payments/Payment.php
+++ b/src/Payments/Payment.php
@@ -102,7 +102,9 @@ public function setGateway(string $gateway)
      */
     public function setParameter($key, $value)
     {
-        $this->parameters[$key] = $value;
+        $params = $this->parameters;
+        $params[$key] = $value;
+        $this->parameters = $params;
         $this->save();
     }
 
diff --git a/src/Requests/AbstractRequest.php b/src/Requests/AbstractRequest.php
index a323e40..c3d6888 100644
--- a/src/Requests/AbstractRequest.php
+++ b/src/Requests/AbstractRequest.php
@@ -166,7 +166,7 @@ private function validate()
      * @param string[] $args
      * @throws InvalidRequestException
      */
-    private function validateParameters(...$args)
+    private function validateParameters(array $args)
     {
         foreach ($args as $key) {
             $value = $this->parameters[$key];
diff --git a/src/Responses/AbstractValidatePaymentResponse.php b/src/Responses/AbstractValidatePaymentResponse.php
index ba0ab32..a82c2c8 100644
--- a/src/Responses/AbstractValidatePaymentResponse.php
+++ b/src/Responses/AbstractValidatePaymentResponse.php
@@ -15,4 +15,9 @@ public abstract function getGatewayId();
      */
     public abstract function validated();
 
+    /**
+     * @return string
+     */
+    public abstract function getMessage();
+
 }
\ No newline at end of file