Please ensure the campaign has been enabled by toggling the switch in the top-right corner of the campaign screen from "off" to "on." This is required in order for the blast to send.
If you duplicated the campaign from a previous blast, it’s possible that it may not send due to updates made since the original campaign was created. In this case, we recommend creating a new campaign from scratch and attempting to send it again.
Campaigns - Blast Campaign - Why isn’t my Blast campaign sending?
Updated over a month ago