I keep getting an error: "RestException: [HTTP 400] Unable to create record: The 'To'..."

when trying to use a variable - see below, example = $user_phone_number = "+13334445555"

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$client = new Client($account_sid, $auth_token);
      
$client->messages->create(
  // Where to send a text message (your cell phone?)
  $user_phone_number,
  array(
   'from' => $twilio_number,
   'body' => $MsgBody
  )
);
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