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1. It seems that i have 1.7.1 version of the plugin and you have here 1.7.4. Could that be the problem? Shall i update it ?
2. Indeed there is a fatal error when i enabled debug.log and here is the error:
PHP Fatal error: Uncaught phpmailerException: Invalid address: (addAnAddress to): in /home/oc-includes/vendor/phpmailer/phpmailer/class.phpmailer.php