heroku config vars to set emails for nodemailer

I am on a nodejs app, using nodemailer to send emails.
I have set the TO emails in the heroku environment like the following:

TO_EMAILS

and the value is:

"['email1@gmail.com', 'email2@gmail.com']"

however, when I receive the email, i get the email for the first one email1@gmail.com and nothing to the second one. However, the name of this first email appears as ['', 'email2@gmail.com']

How can I set the variable so that I get the email sent to both email addresses?

via Bonnard