Strange behavior when using the 3 parameter keys

Hi, I have a problem and a doubt at the same time.
My Environment
wordpress 6.0
Metabox 5.6.4
Custom Table 2.1.1

First, what is the purpose of the third parameter Key
MB_Custom_Table_API::create( $table_name, $columns, $keys = array() ); I may be missing something in the translation into my language.

Now I see a problem, I'm using the example in the documentation with the address-phone-email fields and the key email parameter, but when I have the keys parameter enabled when saving a post the fields are not saved in the database, and when remove the optional key field the data is saved normally.

Regards, Luiz Araujo