Paypal — cashback voucher not given

Sir i purchase on myntra and pay through paypal. There is an offer to cashback voucher of rs.500 bt they don't give me. I try to contact it bt they don't repy satisfactory answer.
They message your transaction is not eligible nd when i asked why then they replied "i am sorry i cant disclose for what reason this transaction is not eligible."
Transaction i'd -2ml16727vn079753g
Date of purchase[protected]
Amt-3278