Ensure that the Delivra opt-in button is added to your layout profiles. Opt-in field should appear automatically within 10 minutes of installing package. To manually add the opt-in field:
Repeat for Leads
Update all contacts/leads that will be synced to have the Delive Opt-in box checked: https://help.salesforce.com/articleView?id=000315142&language=en_US&type=1&mode=1
To speed up first sync, consider using Delivra's CSV import feature to import your contacts initial data. This will speed up your initial sync as the records will already belong in Delivra.