Hi, I’ve tried just now but I’m unable to reproduce the error. Could you kindly reported the error details?
If the error has been intercepted by WP, it should have been sent to the administration email (the one set on the main WP settings).
If there is no email, the server error logs should contain the details.
Another way is to set the Newsletter plugin in debug mode, there is an option on Newsletter’s main settings (note: it’s not the logging level, it’s a setting specific for the debug mode).
Once active a notice is shown on top of our administration pages.
Them if you reproduce the error, a log file should be available under Help/Logs with name php-xxx.log.