ReferenceError: ignore_9mail is not defined

Sending email through the plugin doesn’t work. I receive this error from the log: ReferenceError: ignore_9mail is not defined.

After approaching server support (cloudways.com) using elastic email, this is their answer:
Upon review of the message example you shared, we see that the parsed body for it includes a “” value which is causing the error. The “reference error” is related to template scripting – simple programming that we use in templates optionally. Template scripting is enclosed in double curly brackets . It’s most likely they were put in by mistake when you actually intended to use merge fields there – single curly brackets { }.
Please double-check the HTML code of your email template and remove double curly brackets into single curly brackets.