If you are just inserting the variables and they are not part of the original email template - this won’t work. This is improved in OJS 3.4 though, and users are able to more easily insert content to fit their needs: https://docs.pkp.sfu.ca/learning-ojs/en/about-ojs#workflow (the section header that starts " Enhanced email template tools" - is the most relevant for the purposes of this discussion)