There are several factors that could contribute to Facebook reporting more sales than you get in Shopify. Here are a few things you can do to investigate the issue:
Verify the accuracy of your Shopify data: Make sure that your Shopify store is properly tracking all of your sales. Check your settings and make sure that all necessary data points are being captured.
Check the attribution: Facebook ads can be attributed to sales that take place outside of Shopify. For example, if a customer clicks on a Facebook ad and then makes a purchase on your website at a later time, that sale may not be attributed to Facebook in Shopify. You can use Facebook's own analytics tools to cross-check whether the conversions are actually happening or not.
Look into discrepancies in reporting: Sometimes reporting discrepancies can occur due to differences in the way that Facebook and Shopify measure sales. Facebook may count sales differently than Shopify does, and this could cause a difference in reported sales numbers. This is something that you can investigate further by looking into the specific metrics that are being reported by each platform.
Seek professional help: If you're still having trouble figuring out why Facebook is reporting more sales than you get in Shopify, consider seeking professional help from an e-commerce consultant or marketing agency.
In any case, it's important to ensure that you have a clear understanding of where your sales are coming from and how they are being tracked. This will help you make informed decisions about your marketing and sales strategies moving forward.