New API Sign-up Unit: Do you need a completely new Welcome Journey or Offer for this campaign? If so, you'll want to create a new API Sign-up Unit.
Reuse existing API Sign-up Unit: Is the Welcome Journey or Offer you want to use, one that you've created an API Sign-up Unit for previously? If so, you can reuse an existing API Sign-up Unit.
Example: You already have an API Sign-up Unit for Giveaway Entries, so you can use it again.
This process involves the Attentive White Glove team. See here the full, step by step instructions.
Navigate to Sign-up Unit
Scroll down and copy the ID of the Marketing API. You can then paste it into your HiTide Campaign.