Can not upload sftp

Hi,

I just installed the uFTP app to my Meizu Pro 5 phone on OTA-11.
I can set up a SFTP connection to a desktop machine (Kubuntu), and explore the file system. I can download any files to the Ubuntu Phone.
However when I try to select a file from the phone to upload to the Kubuntu machine the phone reports that it's "unable to upload the file".

I have tried to upload files from the downloads cache in uFTP or off the SD card

I click on my pre set up server. Explore the file system. Select Downloads. Create new folder "Test". Select Test.
On the phone click black "up" arrow at top right.
Choose File Manager. Go to Downloads or SD card. Click on an mp4 file. Press Select.

"Upload 1 file?"
Choose OK.

Response
"Unable to upload the file. OK"

Same result if I go to Document Viewer and choose a pdf file or any other file.

I am using a non standard SSH port. But get the same result if I change to port 22.

Did I do something wrong?

I was not yet able to connect to my desktop machine by FTP to see if FTP upload works..

Filezilla on my desktop machine works very well to and from the phone.

Andrew