It is possible to sign in to Day One Sync with Apple ID. This is to help users sign in without having to remember yet another login.
Day One Android does not support signing in with Apple ID. Also, if you have multiple devices with different Apple IDs, you can use these steps to add an email address to your existing account with Apple ID.
- Go to http://dayone.me/user/login
- Click the link to Authenticate with Apple ID
3. Log in with your Apple ID.
4. Click Account at the top
5. Add/update email address - follow on-screen prompts
6. Add/change password
Now you can use that email and password to sign in with you choose "Day One account" to sign in on the apps.