Key contains a dot which is not supported.

Problem/Motivation

I get this error when I try to add a flag module action.
Any idea, please? Thanks

The website encountered an unexpected error. Try again later.
Drupal\Core\Config\ConfigValueException: flag_action.bookmark_flag key contains a dot which is not supported. in Drupal\Core\Config\ConfigBase->validateKeys() (line 209 of core/lib/Drupal/Core/Config/ConfigBase.php).