I submitted a book chapter, and the references did not appear, although I added the DOI of it, and the references were mentioned on the page of this chapter
I guess you mean https://www.researchgate.net/publication/379190219. Indeed, ResearchGate's automated algorithm did not recognize the references. This algorithm is generally far from being perfect. Many references are not or wrongly recognized. You may try to apply the method developed by Andrejs Krauklis : https://www.researchgate.net/post/Method_for_Improving_Recognition_of_Citations_References_on_ResearchGate/1. However, my experience is that it works only prior to uploading the public file, see also the discussion therein. But you may try, and perhaps the references will be recognized.