Writing a chapter for an open-access book is the same as for a book not available for free. It is just the financing model which differs. The question is who will pay for the publication. If they demand a fee from the authors, you should decide whether it is worth to pay. And you should carefully check the reputation of the publisher. Rather often such offers come from predatory publishers. In this case (https://www.intechopen.com/welcome/79498309dfe498775b2ca112a4787196), the publisher seems to be a predatory one, see https://www.researchgate.net/post/What_is_InTech_Open_Science_A_predatory_or_a_ligitimate_publisher.