You're receiving the error message "Tried to send promotional email to recipient without opt-in" when attempting to send emails in Marketing Cloud Next.
The most common reason to see this error is if you have not imported consent. Consent is not default "opted in" so it must be imported. You can check on an individual record's consent using instructions in this article.
Another common problem is seeing this error when sending transactional emails.
There is a common misconception that disabling Require transactional email messages to use communication subscriptions to validate consent setting in Marketing Cloud means that all transactional emails will not check for consent. This is not correct.
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