Why am I seeing duplicated purchases in Ads Manager with Pixel/CAPI?

[Mimimonzon]

Hi there!

I have two questions around pixel/CAPI for Shopify.

I currently have one pixel associated to my ad account, I've added Facebook pixel, Conversions API app to track conversions and everything seems to be well connected since I'm reporting Purchases.

However, I've been getting Purchases duplicated in Ads manager.

For example, I see 1 purchase in coming through at 8am in Shopify and in Ads Manager I see 2 coming at 8am. 

1. Is there any reason why I could get Purchases duplicated?

2. Why does Shopify create a Data Set ID when I created the Shopify page? I'm asking because there was a data set ID firing in Purchase thank you page, along with my pixel and I deactivated it from Adtrace. Is this data set ID necessary?

Thank you!

Mimi