Office.js: MakeEWSRequestAsync throws “The request exceeds the 1 MB size limit. Please modify your EWS request”

One of my customer created Outlook Web add-in (Office.js) and when he calls mailbox.makeEwsRequestAsync method. But they got the following error “The request exceeds the 1 MB size limit. Please modify your EWS request”. At the app level, the developer is making the call from web add-in to create a mail item in drafts folder…