How did you "create" the email? Was it a newsletter, just a new mail from the "Email Queue" module, or one from API?
I'm not 100% sure on the specifics on what is, but I'm quite sure the free edition doesn't support this feature.
In v12 the free edition only supported 1 newsletter and no email campaigns. You could reach out to email@example.com to let them confirm what you could do.