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What does the iPhone error message "CardDAV Account Verification Failed" mean?

sync.blue®
Updated

If you receive the message “CardDAV Account Verification Failed” on your iPhone or iPad, it means that your device cannot establish a secure connection to the sync.blue® server. This is usually due to incorrect login credentials, an incorrect server address, or missing authorization in your sync.blue® profile.

Possible Causes

  • Incorrect server URL: The URL was probably entered incorrectly.

  • Incorrect login credentials: Username or password were not entered or transferred correctly.

  • DNS issues: The DNS server of your network cannot resolve the server’s address.

  • Missing SSL encryption: The device is trying to establish an unencrypted connection, which is rejected by the server.

 

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Scenario A: Incorrect Input Data

This is the most common cause. The data stored on the device does not match the server requirements.

Solution:

  1. Navigate to your CardDAV account in the iPhone settings.

  2. Completely delete the entries for Server, Username and Password.

  3. Manually re-enter the data (avoid copy/paste to prevent spaces).

 

Scenario B: Network or DNS Issues

In this case, your iPhone cannot technically reach the server, even though the data is correct.

Solution:

  1. Check if you can access the URL https://carddav.sync.blue/<MOBILE Storage API-Key>/addressbook in the browser of the affected device.

  2. If you receive an error message in the browser, try using mobile data (instead of Wi-Fi) to rule out a local DNS error.

 

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Scenario C: SSL Certificate Error in Corporate Network

If you are in a secured corporate network, additional security barriers may block the connection.

  1. Contact your IT department to check if access to carddav.sync.blue via port 443 is allowed.

  2. Make sure that Use SSL is enabled in the advanced account settings of the iPhone.

 

Universal Solution: Restart the Setup

If the scenarios listed above do not directly resolve the issue, the following step is recommended:

  • Procedure: Cancel the current CardDAV account setup completely and start the process again. A clean reinstallation often resolves minor synchronization conflicts.

 

 

 

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