Can I add a co-author who doesn't have an Apiway account?

No — co-authors must already have a **published** creator profile on Apiway, because the credit split goes to their account automatically every time a brand uses the listing. The Apiway team needs a real account to credit. If your photographer or stylist is not on Apiway yet, ask them to sign up, claim a nickname, and publish a minimal profile first; then you can add them by nickname when listing the photo set.