title: ADF expression adddays() giving error "The datetime string must match ISO 8601 format"
body: <p>for ADF parameter I provided <code>@{formatDateTime(adddays(utcnow(),-5),'yyyy-MM-01'))</code> in Debug/trigger but I get this error.</p>
  <p>In function 'formatDateTime', the value provided for date time string '@{formatDateTime(adddays(utcnow(),-5),'yyyy-MM-01')) ' was not valid. The datetime string must match ISO 8601 format</p>
  <p>I have also tried these and it does not work.</p>
  <pre><code>@adddays(utcnow('yyyy-MM-dd'),1)
  @{formatDateTime(adddays('2021-02-09T08:40:00.4158787Z',-5),'yyyy-MM-01'))
  @{formatDateTime(adddays('2021-02-09T08:40:00.4158787Z',-5),'yyyy-MM-ddTHH:mm:ss:fffffffK'))
  </code></pre>