title: S3 CreateEventSourceMapping triggers "Operation not found" error
body: <p>I'm trying to create source maps so when someone uploads something inside the bucket, Lambda will trigger a previously created function, as described <a href="https://docs.aws.amazon.com/lambda/latest/dg/API_CreateEventSourceMapping.html" rel="nofollow noreferrer">here</a></p>
  
  <p>But, when I call this:</p>
  
  <pre><code>$fnName = 'my_function';
  $s3-&gt;createEventSourceMapping([
      //'BatchSize' =&gt; &lt;integer&gt;,
      'Enabled' =&gt; true, //&lt;boolean&gt;
      'EventSourceArn' =&gt; 'arn:aws:s3:::'.S3_BUCKET.'/'.$fnName, // REQUIRED
      'FunctionName' =&gt; $fnName, // REQUIRED
      'StartingPosition' =&gt; 'LATEST', //'TRIM_HORIZON|LATEST|AT_TIMESTAMP',
      //'StartingPositionTimestamp' =&gt; &lt;integer || string || DateTime&gt;,
  ]);
  </code></pre>
  
  <p>I get the following error message <code>Operation not found: CreateEventSourceMapping</code>.</p>
  
  <p>Some of those parameters are not active because according to the documentation found in <a href="https://docs.aws.amazon.com/aws-sdk-php/v3/api/api-lambda-2015-03-31.html#createeventsourcemapping" rel="nofollow noreferrer">https://docs.aws.amazon.com/aws-sdk-php/v3/api/api-lambda-2015-03-31.html#createeventsourcemapping</a> they have default values or aren't required (as far as I undestand)</p>
  
  <p>At the moment I am using PHP SDK (ver 3.94.2). Is there something I am missing?</p>