How to sync contacts with Apple iPhone (iOS)?

Solution 1: via Apple iCloud

Use the "Apple iCloud" application to synchronize contacts with the iPhone. The prerequisite is that iCloud contacts have been activated on the iPhone.

Solution 2: via CardDAV

On the iPhone:

• Open Settings -> Contacts -> Accounts -> Add Account
• Enter:
  • Server: directory.sync.blue
  • Username: API_KEY (replace with your own API Key, which is displayed when setting up a sync.blue® connection)
  • Password: API_KEY (as in Username)
  • Description: sync.blue
  • Advanced Settings
    • Use SSL: yes
    • Port: 443
    • Account URL: https://directory.sync.blue/API_KEY

Solution 3: via Microsoft 365 / Windows Live

After adding the account, the contacts are natively synchronized with the smartphone including subfolders.