If your Shopping Cart or Processor sends the main sale webhook notification separately than your upsell transactions this can lead to what "may seem" as an over-reporting of conversions.
There is an easy fix:
- Go to the Setings > Payment Processing and Carts.
- Select your cart or processor the webhook is set up in.
- Select the webhook in question and click the Edit icon:

- Switch the "Record Unique Conversions Only" switch ON:

- The switch will turn Blue, indicating it is ON, when done, hit Save & Generate Webhook URL:

This will ensure that only one unique conversion is recorded per customer while properly adding and recording the revenue from all main sales and upsells moving forward.
Note: This setting will only record unique conversions moving forward and not retroactively.