custom field not showing in admin notification

Hi. Could you help me with this?
I created a custom field: “Add Me to the Mailing List” as a check box. This produced the data base key of”rpr_add_me_to_the_mailing_list”.
Within the Custom Admin Notification box, I have this:
New user registered on your site %blogname%

Username: %user_login%
E-mail: %user_email%
Maillist: %rpr_add_me_to_the_mailing_list%
Firstname: %first_name%
Lastname: %last_name%

However, for my custom field, the result I get in my Admin Notification is blank. There is not “yes” or “no” or indicator that the box was checked.

https://www.ads-software.com/plugins/register-plus-redux/