Hi ​@karoshino 

Thank you for posting in the community!

If you already have your flow set up and want to send a welcome message including a double opt-in, I’d recommend the following:

First of all, create a segment with profiles who subscribed earlier but have received zero emails. Then export this segment to a CSV file - you don’t need to include anything besides their unique identifier, which is typically just their email address.

Before re-uploading, make sure your confirmation message is tailored to this segment opting in again. You can edit this under your list settings, where the double opt-in message is customizable.

When uploading the CSV to your list, you’ll be asked, “How did you collect consent?” - and this part is important: don’t select “subscribed” if you want them to receive the confirmation email. Choosing “subscribed” skips the double opt-in process entirely.

Once uploaded correctly, the confirmation email will be triggered, and they’ll be able to receive emails going forward.

I hope this helps! Otherwise let me know - I’ll be happy to clarify to help you succeed.

Thanks, very helpful.
It worked after I realized that I needed to delete the people on the list that never received an email prior to importing the CSV.