SFTP over OpenSSH server doesn't work

I choose AFM as a client for my smartphone to exchange files with my laptop.
A connection has been created to authenticate with privkey, and when is established, it correctly chroots the folder indicated in sshd_config
Problems come at this point, when I select copy from some file's 3-point menu, and paste it on the other side of the connection, either way.
See screenshot for message error,

The same server/user config is working fine with total command on an android tablet
Anyway, I am going to attach a part of the sshd log since I notice that there is no entry with scp command or other file operation
https://pastebin.com/RSz4EMUZ

• Device: Huawei P40 Pro
• OS: EMUI 12
• Rooted: No
• Version:

Thank you. This app is very nice, I hope to use it for this purpose.