Subscription is failed to provision. The following records are displayed under
Top > Configuration Director > Logging and Errors > Action Log:
#123456 Provision client to Plesk Process provisioning for document; Failed to create account on Plesk node: Unable to set "locale" argument's value ("en-US"): The specified language pack is installed but not enabled in the system. See Problem # p2016-10-24_23-07-27 for details.
Note: the locale may be different in your case.
Language set under
Top > Account Director > Customer Manager > <Customer_name> > Notifications tab is not enabled on Plesk side.
Either enable appropriate language on Plesk side or change the language for affected account on OBAS side under
Top > Account Director > Customer Manager > <Customer_name> > Notifications tab.