You can reboot your Vobot and see if your Vobot can play songs from your library now.
If this doesn't work:
1. Please update your VOBOT to the latest version
2. Cancel the authorization of alexa and then authorize it again. (Please refer to Why cannot play Amazon Prime Music? to see the authorization process)
3. Make sure that the account which you authorized with Amazon is the same one that has your amazon music access.