You can add contributors to projects from the contributors tab within the project.

Open the project you would like to invite people into.
Click on contributors from the menu on the top, just under the project name.
Click add someone to choose the contributor(s) you want to invite to that specific project.

Ensure you have setup their permissions correctly from Settings > Permissions.
You can add anyone to a project but you can only colloprate with people who've you invited into your business.
Was this article helpful?
Thank you!