If you're having some trouble connecting your iCloud calendar to Acuity, be sure you're using your iCloud user name and password when connecting. You can double check your login information at https://icloud.com. If you've enabled two-factor authentication in iCloud, you'll need to create an app-specific password just for Acuity. If you aren't sure if you've enabled two-factor authentication, give the below steps a shot -- a lot of times, this will solve any connection issues!
Create an App-Specific Password for Acuity:
- Pull up your Apple ID account page
- Under Security > App-Specific Passwords, click "Generate Password" and follow the steps
- Use the password when connecting Acuity and iCloud.
You can read more on that in Apple's help article Using App-specific Passwords.
Also, keep in mind that iCloud events 200 days into the future will sync once this is set up.