ftp permissions

644 means that files are readable and writeable by the owner of the file and readable by users in the group owner of that file and readable by everyone else.

755 is the same thing, it just has the execute bit set for everyone. The execute bit is needed to be able to change into the directory. This is why directories are commonly set to 755.

https://forums.cpanel.net/threads/why-are-644-and-755-unix-permissions-ideal-for-files-directories-in-public-folders.136821/