this is because FB uses attribution window for attributing the purchases to the ads you run.
The default attribution model on FB is 1-day after view and 7-day after click.
Let me explain this: If a user clicks on your ad today and is redirected to your website, surfs the website but doesn’t make purchase today but comes back within the following 7 days, FB will attributes a purchase to this ad. Therefore, you can see differences in the analytics.
I would trust the real number of made purchases, hence the real number you see in your Shopify store account.
Hi @Kelliev ,
Facebook duplicate conversions is a known issue that makes it hard for you to really measure your advertising performance and ROAS accurately. It can happen due to various reasons, customers that refreshed the checkout page, clicked and/or viewed more than one ad in the attribution window and the list goes on...
We developed on AdScale a report that helps you to eliminate the double conversions by connecting the conversion ID directly to the Shopify Order ID, and this can detect duplicate conversions on Facebook & Instagram, or even cross-platfrom between Facebook & Google. This way you can get the real picture of your advertising performance!