Put issue module 3

ftp> put ~/workspace/ftp_client/upload.txt ~/workspace/ftp_server/upload.txt
local: /home/crio-user/workspace/ftp_client/upload.txt remote: ~/workspace/ftp_server/upload.txt
227 Entering Passive Mode (127,0,0,1,223,124).
553 Could not create file.

check if write_enable=YES is set in vsftpd.conf file. (am assuming your upload.txt file has write permission)

see this too. FTP : 500 OOPS: vsftpd: cannot locate user specified in 'ftp_username':ftp (use this only to ensure your changes are effective. other things doesn’t matter)

after that try uploading file again.