If you see a "Access Denied" error, this would indicate that you have enabled a splash page in Datto Networking but have not saved the splash page.
Simply navigate to the SSID #1 tab and open the splash page editor. Once you have done this, make sure that you click the floppy disk icon ("Save"), as this will save your splash page to your network. After you have saved your splash page, simply close the splash page editor, and click "Update Network Settings" to ensure your access points have updated with this recent configuration change.
What Do the LED Indicators Mean on Series 3 Datto Devices?