The tracking in my Facebook Pixels across multiple sites is off in Ads Manager when compared to site

[jallard]

I have the new CAPI app installed on multiple sites, but it's consistently sending data back at a different amount than I'm seeing in the stores. To use as an example, one site I'm currently working on, all traffic is going through Facebook, but not all the purchases are being attributed in Ads Manager (in the store itself they're being marked as Facebook in the Conversion Summary).

Has anyone else been having this issue? If so, how can I fix this?