Why don’t contacts enter my Mailchimp Customer Journey when I import them with the trigger tag?

The tag by itself isn't enough unless it's the journey's actual starting trigger and the journey is turned on. Check that the flow uses the same audience you imported into, its first trigger is `Tag added` with the exact tag, and the flow is active. Then test with one brand-new contact: import or add the contact, then apply the tag after the flow is on. Mailchimp only starts people as they meet the first trigger condition, so that clean test usually tells you whether this is a trigger setup issue or an existing-contact issue.