If you added new contacts to a group that is already subscribed to a campaign, you must manually subscribe the missing group members to the ongoing campaign.
IMPORTANT: Ensure all your contacts are placed into the appropriate group. Then, follow the steps below:
Select "My Campaigns" from the left-hand menu.
Navigate to the campaign you want to subscribe the new group members to.
Select the Groups tab on the campaign page.
On the Groups page, you will see a list of all the groups that are already subscribed to the campaign. Each group with any new contacts that have not been subscribed will display the number of missing members in the column to the right.
To subscribe new contacts, click the plus sign button next to the number of missing contacts.
All set! The new contacts will be subscribed to the campaign and will receive the first email of the series within the hour they are subscribed.