It sounds like UpdraftPlus can connect but isn’t able to create or write files on your FTP server. In most cases, this happens because the remote path (the folder path entered in the FTP settings) is incorrect or doesn’t have write permissions.
Please double-check or try adjusting the remote path — for example, if it’s currently /, try something like /public_html/ or /backups/ (depending on your host’s setup). Also, make sure the FTP user has full write access to that folder.
@bcrodua that makes no sense. As I wrote, I log in with exactly the same credentials in a FTP client and can upload anything I want there. It is a public folder – ReFrame is the directory in which the WordPress installation resides. And the images in this thread.