If you have more than one Apple ID, enter the password for the Apple ID you use with iCloud. In the dialog that appears, enter your Apple ID password, then click Allow. Choose Apple menu > > System Preferences > iCloud. If you do receive the previously mentioned notification, click Continue.
Instead, when you set up iCloud Keychain on another device, you allow it to use your iCloud data simply by entering the login password or passcode for a Mac or iOS device that already has your iCloud Keychain set up. You don’t receive the notification, and you don’t follow the steps below if your Apple ID uses two-factor authentication. If you set up iCloud on this Mac, and then you set it up on another device, you may receive a notification on this Mac telling you that the other device wants to use your iCloud account. If you aren’t signed in to iCloud already, you must set up iCloud before you can select Keychain.
