GrabzIt's API allows you to convert up to 15 MB of HTML into a single document or image. Unfortunately this limit can not be raised any further. If you try to convert more HTML than this limit you will receive the Maximum size of request reached error.
The first approach we would recommend is that you try to compress the HTML. Remove any redundant comments, spaces, attributes, hidden inputs and HTML elements etc that won't alter how the document is displayed.
Alternatively, if you are converting your HTML into a DOCX or PDF document and have tried to compress your HTML but are still above the 15 MB limit then you can split the HTML into smaller pieces and convert each piece separately. Then merge the pieces back into a single document.