diff --git a/src/ARBUpdateSubscriptionRequest.php b/src/ARBUpdateSubscriptionRequest.php
index 32c0054..e5bb726 100644
--- a/src/ARBUpdateSubscriptionRequest.php
+++ b/src/ARBUpdateSubscriptionRequest.php
@@ -16,14 +16,18 @@ class ARBUpdateSubscriptionRequest extends ARBCreateSubscriptionRequest
     public function __construct(
         Configuration $configuration,
         Client $client,
-        $subscriptionId
+        Subscription $subscription,
+        string $subscriptionId
     ) {
-        parent::__construct($configuration, $client);
-        $this->subscriptionId = $subscription;
+        $this->subscriptionId = $subscriptionId;
+        // Authnet does not allow an interval to be updated
+        $subscription->removeInterval();
+        parent::__construct($configuration, $client, $subscription);
     }
 
     protected function attachData(RequestInterface $request)
     {
         $request->addData('subscriptionId', $this->subscriptionId);
+        parent::attachData($request);
     }
 }
diff --git a/src/DataTypes/ArbTransaction.php b/src/DataTypes/ArbTransaction.php
new file mode 100644
index 0000000..3196fce
--- /dev/null
+++ b/src/DataTypes/ArbTransaction.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace CommerceGuys\AuthNet\DataTypes;
+
+class ArbTransaction extends BaseDataType {
+    protected $propertyMap = [
+        'transId',
+        'response',
+        'submitTimeUTC',
+        'payNum',
+        'attemptNum',
+    ];
+}
diff --git a/src/DataTypes/Interval.php b/src/DataTypes/Interval.php
index dd0e341..9b00cdd 100644
--- a/src/DataTypes/Interval.php
+++ b/src/DataTypes/Interval.php
@@ -23,7 +23,7 @@ protected function validate(array $values)
             throw new \InvalidArgumentException('Interval must have a unit.');
         }
         if (!array_intersect(['days', 'months'], (array) $values['unit'])) {
-            throw new \InvalidArgumentException('Interval unit must be days or months.');
+            throw new \InvalidArgumentException('Interval unit must be days or months.' . $values['unit']);
         }
         switch ($values['unit']) {
             case 'days':
@@ -41,4 +41,14 @@ protected function validate(array $values)
                 break;
         }
     }
+
+    public function addLength(int $length)
+    {
+        $this->propertyMap['length'] = $length;
+    }
+
+    public function addUnit(String $unit)
+    {
+        $this->propertyMap['unit'] = $unit;
+    }
 }
diff --git a/src/DataTypes/PaymentSchedule.php b/src/DataTypes/PaymentSchedule.php
index 9b33f66..d0f9baa 100644
--- a/src/DataTypes/PaymentSchedule.php
+++ b/src/DataTypes/PaymentSchedule.php
@@ -15,4 +15,13 @@ public function addInterval(Interval $interval)
     {
         $this->properties['interval'] = $interval->toArray();
     }
+
+    public function addTotalOccurrences(String $totalOccurrences)
+    {
+        $this->properties['totalOccurrences'] = $totalOccurrences;
+    }
+
+    public function addStartDate(string $startDate) {
+        $this->properties['startDate'] = $startDate;
+    }
 }
diff --git a/src/DataTypes/Subscription.php b/src/DataTypes/Subscription.php
index 133263b..834a7ae 100644
--- a/src/DataTypes/Subscription.php
+++ b/src/DataTypes/Subscription.php
@@ -45,4 +45,70 @@ public function addProfile(CustomerProfileId $profile)
     {
         $this->properties['profile'] = $profile->toArray();
     }
+
+    public function addAmount(string $amount)
+    {
+        $this->properties['amount'] = $amount;
+    }
+
+    public function getAmount()
+    {
+        return $this->properties['amount'];
+    }
+
+    public function getInterval() {
+        if(is_array($this->properties['paymentSchedule'])) {
+            return $this->properties['paymentSchedule']['interval'];
+        }
+        return $this->properties['paymentSchedule']->interval;
+    }
+
+    public function getPaymentSchedule() {
+        return $this->properties['paymentSchedule'];
+    }
+
+    public function removeInterval()
+    {
+        unset($this->properties['paymentSchedule']['interval']);
+    }
+
+    public function getStartDate()
+    {
+        if(is_array($this->properties['paymentSchedule'])) {
+            return $this->properties['paymentSchedule']['startDate'];
+        }
+        return $this->properties['paymentSchedule']->startDate;
+    }
+
+    public function addStartDate(string $startDate)
+    {
+        if(is_object($this->properties['paymentSchedule'])) {
+            $this->properties['paymentSchedule']->startDate = $startDate;
+        }
+        $this->properties['paymentSchedule']['startDate'] = $startDate;
+    }
+
+    public function removeStartDate() {
+        unset($this->properties['paymentSchedule']['startDate']);
+    }
+
+    public function getArbTransactions() {
+        return $this->properties['arbTransactions'];
+    }
+
+    public function addArbTransactions($arbTransactions)  {
+        if( is_array($arbTransactions)) {
+            $arbTransactions = $arbTransactions['arbTransaction'];
+        }
+        else {
+            $arbTransactions = $arbTransactions->arbTransaction;
+        }
+        foreach( $arbTransactions as $arbTransaction ) {
+            $this->properties['arbTransactions']['arbTransaction'][] = (array) $arbTransaction;
+        }
+    }
+
+    public function addArbTransaction(ArbTransaction $arbTransaction) {
+        $this->properties['arbTransactions']['arbTransaction'][] = $arbTransaction->toArray();
+    }
 }