Nextcloud’s SMB password field has a nasty habit of rejecting perfectly valid credentials the moment you click ‘verify’. After hours of hair-pulling, I discovered the fix is blissfully simple: skip the broken GUI entirely and add the share directly with OCC commands.
Five lines in the terminal later, your share mounts perfectly, users get access, and you can get on with your life. No tickets, no forum threads, no sacrificing a goat to the SMB gods required.