You can give a try to Flexify app
Well, there can be multiple reasons for it but when it comes to pixel, I would recommend first check whether the right pixel is connected to your Shopify store or not.
After that, I wanted to give you an update, which is that Shopify right now is working on its updates and so no user will be able to create a Facebook or Instagram shop.
But, if you're adding it manually, then you must be having a CSV file downloaded from your Shopify store. If you don't have a CSV file, then you can follow these steps:
1) Click on products.
2) Click export.
3) From the dialog box, choose the products you want to export.
4) Select which type of CSV file you want to export, such as, for Excel, Numbers, or another spreadsheet program.
Also, in order to fully understand the problem, it's necessary to see the problem by ourselves to figure out the exact solution.
I hope this helps.