Cannot backup to offsite NAS.

[SirMacke]

So, I got an old Qnap TS-109 1TB for having a offsite backup for my AS-1002T

I have a FTP-backup-job, but it fails.

Failed to to upload file(/volume1/NAS/Foto/Bröllop/Bröllopsfotografering.zip): Upload failed (at start/before it took off)(550)
File is 460MB, it should not be a problem.
No idea if the error is on the Asustor och Qnap.
Any ideas for solving this?
Or if someone could recommend a 3rd party app for this.
Weekly backup of some folders over ftp.