Looking for logging into the 503 With User First 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 503 With User First site. After that you can login as usual with your login credentials.
https://enterprisedt.com/questions/index.php/2915/can-not-use-connect-command-says-login-with-user-first
https://fetchsoftworks.com/fetch/messageboard/login-with-user-first
https://forums.iis.net/t/prev/1169922
https://forum.filezilla-project.org/viewtopic.php?t=24336
https://serverfault.com/questions/292322/ftp-user-isolation-issues
https://www.corenetworkz.com/2011/05/ftp-error-503-login-authentication.html
http://loginee.com/503-with-user-first
https://bobcares.com/blog/why-you-get-530-login-authentication-failed-in-your-cpanel-pure-ftpd-ftp-server/
https://community.hpe.com/t5/System-Administration/ftp-error-503-user-access-denied/td-p/2869886
https://www.smartftp.com/forums/viewtopic.php?t=10786
https://bugzilla.redhat.com/show_bug.cgi?id=483604
https://www.inmotionhosting.com/support/community-support/file-management/how-can-i-connect-via-ftp-using-filezilla-i-get-a-530-error
https://stackoverflow.com/questions/3355848/ftp-error-530-user-cannot-login