[Samba] Cannot raise the domain functional level to 2012_R2

[shacky]

Hi,
according to https://wiki.samba.org/index.php/Raising_the_Functional_Levels
the functional level 2012_R2 should be supported on Samba 4.4 and later.

I have Samba 4.11.6:
========================================================
root at server-z1:~# smbd -V
Version 4.11.6-Ubuntu
========================================================

My actual functional level is 2008_R2:
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root at server-z1:~# samba-tool domain level show
ldb_wrap open of secrets.ldb
Domain and forest function level for domain 'DC=my,DC=domain,DC=local'

Forest function level: (Windows) 2008 R2
Domain function level: (Windows) 2008 R2
Lowest function level of a DC: (Windows) 2008 R2
========================================================

But I cannot raise to 2012 or 2012_R2:
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root at server-z1:~# samba-tool domain level raise --domain-level=2012
ldb_wrap open of secrets.ldb
ERROR: Domain function level can't be higher than the lowest function level
of a DC!

root at server-z1:~# samba-tool domain level raise --domain-level=2012_R2
ldb_wrap open of secrets.ldb
ERROR: Domain function level can't be higher than the lowest function level
of a DC!
========================================================

The same trying to do it using Active Directory Domains and Trusts.

Could you help me to understand where I'm wrong, please?

Thank you very much!
Bye