Cannot backup to external server over ssh

[klabacita]

Hello.

I have setup auto_backup latest version(15.x) under ubuntu 20.04.1 LTS.
Local backups is working, the issue I have is that I cannot backup a external server over ssh.
I had setup ssh in both servers with public key, I can test in shell in both sides and I can access the shell without password.
But, once I setup auto_backup for external backup, I receive this error:

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/odoo/addons/base/models/ir_http.py", line 237, in _dispatch
result = request.dispatch()
File "/usr/lib/python3/dist-packages/odoo/http.py", line 687, in dispatch
result = self._call_function(**self.params)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 359, in _call_function
return checked_call(self.db, *args, **kwargs)
File "/usr/lib/python3/dist-packages/odoo/service/model.py", line 94, in wrapper
return f(dbname, *args, **kwargs)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 348, in checked_call
result = self.endpoint(*a, **kw)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 916, in call
return self.method(*args, **kw)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 535, in response_wrap
response = f(*args, **kw)
File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1351, in call_button
action = self._call_kw(model, method, args, kwargs)
File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1339, in _call_kw
return call_kw(request.env[model], method, args, kwargs)
File "/usr/lib/python3/dist-packages/odoo/api.py", line 464, in call_kw
result = _call_kw_multi(method, model, args, kwargs)
File "/usr/lib/python3/dist-packages/odoo/api.py", line 451, in _call_kw_multi
result = method(recs, *args, **kwargs)
File "/opt/custom_addons/auto_backup/models/db_backup.py", line 112, in test_sftp_connection
raise Warning(message_title + '\n\n' + message_content + "%s" % str(error))
Exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/odoo/http.py", line 643, in _handle_exception
return super(JsonRequest, self)._handle_exception(exception)
File "/usr/lib/python3/dist-packages/odoo/http.py", line 301, in _handle_exception
raise exception.with_traceback(None) from new_cause
odoo.exceptions.Warning: Connection Test Failed!

Here is what we got instead:
Authentication failed.

paramiko + pysftp are install.

Mark "Autenthicatio failed", any tip or clue where can be the issue to fixit?

Thanks!!!