Remote Backup with rsync - Problems

Hello,
I am using Strato Hidrive for backup and cannot connect, I get an error:

This I entered in the fields:

Remote Backup:    enabled
Temp Folder:    /tmp
Server IP:    rsync.hidrive.strato.com:/users/user0001/server99
Username: user0001
SSH-Port:    22
Access-Key: (generated)

I uploaded the access key to Strato Hidrive.

When I click on "test connection" I get a error, but I think it is because SSH and RSYNC handle directories in a differrent way:
Connection_Failed

Anyone can tell me, what is wrong?
Is there a way to test the remote backup manually with commandline?

Thank you
Kobby

I have checked the access to Hidrive manually:

# rsync -rltD -e "ssh -i /root/.ssh/backup/id_rsa.pub" /backup/ user1@rsync.hidrive.strato.com:/users/user1/server99
Enter passphrase for key '/root/.ssh/backup/id_rsa.pub':
user1@rsync.hidrive.strato.com's password:

-> there is a question for the password of the certificate, but there is no password set during creation of cert
-> there is a question for the password of Hidrive, but there is the certificate

Any ideas?

Generally you have to connect once through cmd as you did and then connection should be automatic, I hope you have transferred the right key ie. /root/.ssh/backup/id_rsa.pub