"Public key for authentication could not be read" message on server's start

[liinahamari]

I receive toast "Public key for authentication could not be read" message on server's start every time. All files access permission been granted as desribed.
From logs file:

starting ftp server
trying authorized keys file /storage/emulated/0/Android/data/org.primftpd/files/.ssh/authorized_keys
could not read key at line 2: java.lang.IllegalArgumentException, bad base-64
could not read key at line 6: java.lang.IllegalArgumentException, bad base-64
trying authorized keys file /storage/emulated/0/.ssh/authorized_keys
Intializing shared thread pool executor with max threads of 10
could not read keys FileNotFoundException, /storage/emulated/0/.ssh/authorized_keys: open failed:...
trying authorized keys file /storage/emulated/0/.ssh/authorized_key.pub
could not read keys FileNotFoundException, /storage/emulated/0/.ssh/authorized_key.pub: open fail...
FTP server started

[wolpi]

That means you don't have a valid key in your file. Can you post file content here?

[liinahamari]

# sample authorized keys file
# place your keys in this file
# one key per line
# of course without leading #
# e.g.
# sh-ed25519 AAAAC3NzaC1lZDI1N....
# ssh-rsa AAAAB3NzaC1yc2EAAAAD...

[wolpi]

That is the automatically generated sample file. Of course it does not contain a valid key. You have to place your key in that file.

[liinahamari]

Is there's an API which helps to do so?

[wolpi]

I don't really understand that question.
Placing a key in a textfile is a common configuration task. If you want to do that programmatically you can just use file APIs.