Can't create new automatic newsletter

I can’t create new automatic newsletter. At first tried modifying the existing sample template, but it wouldn’t save it as automatic and wouldn’t change the title showing two messages at the same time after trying to save it: ‘Newsletter created successfully’ and ‘The newsletter doesn’t exist’. I deleted the template and tried creating a new one, but it wouldn’t create it at all, showing the messages: ‘Newsletter successfully created.
There are no newsletters.’ and ‘The newsletter doesn’t exist.’ I’d appreciate your help.

https://wordpress.org/plugins/wysija-newsletters/