Adding an influencer to your campaign is easy, but you must have added them to 'My Influencer' database first (see this article).
Create a campaign as usual.
Select your influencer to add on the next screen.
At this point the influencer has been ADDED but NOT INVITED. This allows you to set up the campaign and add assets before inviting the influencer to collaborate/authorise data access.
Click on 'Take me to my campaign' button.
'Influencers' tab shows that the influencer is added but not invited.
Invite the influencer by choosing SEND INVITATION from the influencer card.
Once you confirm the invitation, the email will be sent out to the influencer.
Now the influencer can collaborate and authorise.