BE 15 fp 5 backup to the private S3

I'm currently trying to test configuration with backup to our private S3 which is compatible with Amazaon S3 but unfortunately I am unable to complete it.

here is the list of my actions:

1) configure cloud instance using BE MCLI according to BE MCLI *.chm help. It finishes with success.

2) Configure Cloud Storage using BE GUI. All configuration wizard steps completes with success, wizard even successfully retrieves the list of S3 buckets from the S3 service, and completes the configuration with no error.

3) At the end of configuration BE offers to restart it's services to finalize the cloud storage.

4) After the restart device is still shown as offline. There is an alert at the time of services start:

Unable to connect to to the OpenStorage device. Ensure that the network is properly configured between the device and the Backup Exec server.

For more information, see V-275-1017 on the Symantec Knowledge Base.

However, I was unable to find any useful reference in KB to solve this particular issue.

The main question is to understand what is missing from either configuration steps or S3 itself.

Does anyone know how this can be debugged?