Get the reference/experience letter from your employer with job title, duties, dates, hours, and salary, signed on letterhead. Add the cash salary certificate they offered (list amount per month, signed and stamped), plus whatever else you can get: ESIC/PF records, ITR or Form 16 if any, bank statements showing cash deposits around pay dates, appointment letter, ID card, emails. Cash claims get extra scrutiny, so more consistent documents help your case.
