Cloudsync does a shit job of communicating helpful errors. When setting up a new Backblaze configuration with encryption enabled, this was the error: Nothing in UI tools gave me more information, so I ssh’ed in and blindly searched for logs. Turns out the problem is really obvious when you find the actual error. In /var/log/messages this appeared: 2020-04-30T15:15:54-07:00 disko synoscgi_SYNO.CloudSync_1_create_link[29776]: [ERROR] b2-protocol.cpp(1656): B2Protocol: Failed to download file (, error(403), msg({ "code": "download_cap_exceeded", "message": "Cannot download file, download bandwidth or transaction (Class B) cap exceeded.