1. Log in
2. Post > New Work
3. Fill in required information
4. Post Without Preview
5. Add Chapter
6. Check "Add co-authors?" and enter the name of another account you have access to
7. Fill in required information
8. Post Witout Preview
9. Log out
10. Log in with the account you listed as a co-author in step 6
11. Locate and access the work you just created and choose "Edit"
12. On the top of the Edit Work page, where it says "Edit Chapter:", choose "1"
The edit form for the chapter (which is incorrectly labeled as "Post New Chapter") will appear, but at the top of the page will be a red message: "You're not allowed to use that pseud."
Indeed, if you attempt to post edits to the work, you will run into - Chapter co-author trying to edit a chapter they are not a co-author on gives Error 500, so the error message is almost right for the time being. However, is going to be fixed so the co-author can edit the chapter. Ergo:
What should happen instead:
The message "You're not allowed to use that pseud." should not appear.