Facebook says i've had much more add to basket than shopify?

[CatandBear]

I have 2 ads currently running using facebook ad manager. Both live for 1 week.

Ad A according to shopify had 3 ad to basket. According to Facebook ad manager ,this ad had 16 add to basket.

Ad B has 1 ad to basket. According to facebook ad manager, i've had 7 add to basket.

Neither can be true, because according to shopify the total number of add to basket this week is 8.

Has anyone else experienced this? Should I ignore the numbers facebook gives?