Dax Formula returning weird error when multiplying from two tables

There are two tables Invoice detail and Rewards; with many - one relationship. 

Need to create a dax measure two multiply two columns Quantity from Invoice detail and Reward amount from Rewards Table.

Total Rewards = SUMX('invoicedetail', ('invoicedetail'[quantity] * RELATED('Rewards'[Reward_Amount])))

used this dax but it is returning the wrong output.

It is multiplying a quantity by itself and multiplying it to rewards resulting in wrong output.

 

Wrong output : 

It would be great if I could get any help.

Thank you in advance