My SMB-connection on proxmox from Android won’t work

I’ve setup SMB on my proxmox host in order to sync files/pictures/…
When connecting with Android I always get authentication errors.
I’m sure the user/pass are correct.

  • tried different account: same issue
  • tried with “FileManager+”, “Foldersync”, “Solid Explorer”, “Samba Player” > all fail
  • My Android can connect to smb on my windows laptop
  • My Win11 laptop can connect to the proxmox smb share
  • I tried different shares, same issue
  • to rule out firewall I joined the android on the same vlan: same issue
  • i had some succeses with SMB1 if I downgrade the whole smb server (is that an issue on a selfhosted setup?)

Only Foldersync gives longer error messages: “STATUS_LOGON_FAILURE 0xc000006d Authentication failed for ‘username’ using com.hierynomus.smbj,auth.ntlmSealer”; the other apps return ‘Access denied’.

I can’t really find not-super-technical documentation about smb.
Can someone point me to some things I could try or easier documentation?