You may be seeing an "Invalid" message or error icon next to your Apple/iCloud calendar URL:
Follow these steps to regenerate your calendar URL
Login to your iCloud account at https://icloud.com
Click on the Calendar icon
Click on the sharing icon (looks like a wifi icon) next to your calendar name in the left column:
If "Public Calendar" is checked, uncheck it then click OK.
Next click on the sharing icon again and check "Public Calendar". This will generate a new URL.
Click "Copy Link" to copy it to your clipboard, and then paste this new URL into DAKboard.
For more information please see our related article on how to Add your Apple calendar to DAKbaord.