I have been working at a relative's business for the past 1.5 yr. I was not being paid but its a registered company and I can arrange for an official letterhead stating my designation, roles and responsibilities and the time period. There will be no payslips. Would this be enough to prove workex IIM

Dear Rushit, IIMs do not define work experience. And having said that, a mere letter head might not really work because if you have spent a fair period of time working somewhere, you get paid for the efforts you put in. The Selection Committee will verify your service letter which you have. But they will also check your joining letter and last 3 month's pay slips. If you do not have the pay slips, your work experience cannot be vouched for. So you might not have a case there.