CloudBerry Backup / Unraid / B2 ??

Hello,
I am testing before bying CloudBerry Backup running on a Unraid server (docker).
I am able to connect to my Backblaze account (app key ID, bucket name etc.)
When running my backup I have this error message:
an error occured code 1003

Same error if I am backuping a big or small size file.

still preparing for starting …
Syncro stop after 5s … with error

Ideas ?
Thx