We have a chapter in a book, I have tried to added to my RG profile, author of another chapter in the same book used the DOI, I have tried to add my chapter, but RG system says this DOI is already there
The same problem happened to me. It's impossible and RG will display an error message with two solutions; remove it or use the book as reference. But I can't find this book even if it is on RG. How strange! Another pitfall.
There are two ways to do this, one is to try to claim the chapter directly using the instructions under "Help Center" (small font clickable link at the bottom of ResearchGate pages), selecting "Research & Publications", then: How do I confirm authorship of my publications to add them to my profile? Slightly lower down the page, you'll see a link explaining how to add coauthors to your publications. If the methods explained under this information do not work, then I would suggest that you ask your coauthors to add your name to the chapter on their ResearchGate page using "How do I add my co-authors to my publication?". Failing that, contact the ResearchGate staff and wait a few days.