title: Adding to PlayPrefs is Inconsistent Unity Ads
body: <p>I am trying to add coins to my PlayerPrefs after watching an Ad, but the first Reward is 100 coins and then it's getting way more and inconsisten.
  I have no Idea why this problem is occuring.
  Thanks</p>
  <pre><code>public void OnUnityAdsShowComplete(string adUnitId, UnityAdsShowCompletionState showCompletionState)
          {
              float coins = PlayerPrefs.GetFloat(&quot;coinPrefs&quot;);
              if (adUnitId.Equals(_adUnitId) &amp;&amp; showCompletionState.Equals(UnityAdsShowCompletionState.COMPLETED))
              {
                  Debug.Log(&quot;Unity Ads Rewarded Ad Completed&quot;);
                  // Grant a reward.
                  PlayerPrefs.SetFloat(&quot;coinPrefs&quot;, coins + 100);
                  // Load another ad:
                  Advertisement.Load(_adUnitId, this);
              }
          }
  </code></pre>