Abhishek from Addyz ,
Have you setup-ed UTM parameters in your campaigns. If yes, check your Google analytics account and see if you could see matching data there.
If your sales number through fb campaigns is low, there could be some mismatch with number shown up in fb and shopify. As fb claims any order made within 7 days after clicking on the ads.
If you like to automatically setup utm parameters, product feed and use best campaign strategies do checkout our app and you will definitely will see some good results.
if you have any doubts, just comment below and i will be happy to help