Hahahahaha

Thank you very mutch for your answers. =)

I will try again in few days.

Domains settings:

Site ID: 2
Domain: (domain-B)
Primary: yes

Domain Mapping Configuration:

(Server IP Address)
(options 2 & 4, but I tryed multiple options)

Hi !

I just found the solution:

In wp-config.php replace:
define(‘DB_CHARSET’, ‘utf8mb4’);
by
define(‘DB_CHARSET’, ‘utf8’);