Hello! Scopus just register the citation that are in its journal (the journal that are indexing), if the citation is not in some of that journal they are not going to register on your profile. It happens to me, in google academics I have many citations and in Scopus just 1... Sad but real...
Indeed, there is no way to add citations manually. The Scopus database of papers is rather incomplete, and my impression is that they neglect many journals that are not published by Elsevier - perhaps to urge authors to publish in Elsevier journals.
Ingrid Del Valle García Carreño I have already used this service many times. Its very simple. It may take 1-3 weeks to get reply. I have very good experience of the same.
You cannot simply put missing citations in Scopus unless the journals in which your article appeared is in the select list of Scopus for indexing. Scopus database is owned by Elsevier, and they have specific content policy and selection criteria for the journals to be included in Scopus. For more information on journal selection criteria please visit: