Hi,

First we need to check if the contact has confirmed the subscription to the newsletter.
The contact tried to open the voucher without confirming the subscription first. That is why it still 
has the opt_out status due to the fact that after receiving the e-mail, contact did not click on the frame, 
contact did not confirm the subscription to the newsletter and further messages could not be sent due to the lack of consent to the newsletter.
I tested it on my test account and after confirming the subscription to the newsletter, the system automatically assigned me the opt_in status.