According to the google book API documentation, the startIndex can be specified in URL for the start index of the collection(volumes). However, every time I perform the same query with different startIndex, the totalItems from the returned object defers. Not only that, there are always as many as 40 results in the returned object even though the startIndex has already exceeded Math.ceil(data.totalItems / 40(RESULTS_PER_PAGE). Is there anything I am missing for volumes search?

https://www.googleapis.com/books/v1/volumes?q=love+intitle:love&startIndex=0&maxResults=40