Getting error "Permission denied"

[AndreyChursin]

Add to my docker-copmpose.yml

...
sftp:
        image: atmoz/sftp
        container_name: PROJECT-sftp
        volumes:
            - ./sftp/users.conf:/etc/sftp/users.conf:ro
            - ${SITE_PATH}:/home/prog1/www
        ports:
            - '20022:22'
            - '20021:21'
        networks:
            - project_net
        restart: always
...

./sftp/users.conf

prog1:testpass:::www

try sftp prog1@{hostIP} -P 20022 and got error "Permission denied, please try again." host:/var/log/auth.log

Invalid user prog1 from 81.23.125.218 port 61048
pam_unix(sshd:auth): check pass; user unknown
pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=81.23.125.218 
Failed password for invalid user prog1 from 81.23.125.218 port 61048 ssh2

docker-compose logs it's all right, no problems... what i'm doing wrong?