Looking for logging into the 421 Incorrect site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the 421 Incorrect site. After that you can login as usual with your login credentials.
https://forum.filezilla-project.org/viewtopic.php?t=28638
https://www.computing.net/answers/networking/ftp-error-421-login-incorrect/46738.html
https://forums.iis.net/t/1229797.aspx?421+login+incorrect+FTP
https://superuser.com/questions/454274/unable-to-connect-my-filezilla-ftp-server-returns-error-421-login-incorrect
https://www.reddit.com/r/techsupport/comments/3ptzex/im_pretty_sure_im_just_an_idiot_and_cant_port/
https://social.technet.microsoft.com/Forums/ie/en-US/2d941262-a5f8-4658-bfa0-36dfdfaf47a9/unable-to-access-ftp-site-via-internet?forum=winservergen
https://www.hivelocity.net/kb/what-are-the-steps-to-resolve-the-error-421-service-not-available-in-case-of-ftp/
https://bobcares.com/blog/why-you-get-530-login-authentication-failed-in-your-cpanel-pure-ftpd-ftp-server/
https://serversmtp.com/smtp-error/
https://www.siteground.com/kb/common-ftp-errors/
https://support.plesk.com/hc/en-us/articles/115000165425-Unable-to-login-over-FTP-421-Service-not-available-remote-server-has-closed-connection
https://kb.globalscape.com/KnowledgebaseArticle10142.aspx
https://www.ionos.com/help/hosting/setting-up-and-managing-ftp-access/ftp-error-messages-explained/