There are 3 options for Zontracker to activate the ZT-Optimize feature in your FB Business Manager.

Option A (recommended)
Zontracker automatically creates a new Facebook Pixel in your FB Business Manager called "Amazon purchase pixel". Choose Purchase as the conversion optimization event. Make sure it says "Amazon purchase pixel" instead of your default pixel name.

BENEFIT: Simple. Allows use of this feature right away. Amazon purchases will show up in a new column (if you purchased ZT-Track or combo plan). All disadvantages below are only related to metrics you see, performance is unaffected.

DISADVANTAGE: Any type of traffic or campaigns to your website leading to website purchases will NOT track website purchases. This disadvantage is still worthwhile for ability to use the feature and test Amazon purchases in Option A. You will see metrics like cost per click or any action happening on Facebook but you won’t see metrics on the website such as cost per lead/email. If you see traction with this option, then we suggested to implement Option B later. 

Option B (extra steps)
Same as Option A, please read above but only difference is that you take the new pixel (Amazon purchase pixel) and add it to your website. You will have the new pixel and your original pixel on your site.

BENEFIT: Track any type of purchase regardless of what type of traffic or campaign you are running. Having multiple pixels on a site may have other benefits such as segmenting only certain types of data per pixel. See here for advanced implementation or use Trackify for Shopify to have multiple FB pixels.  If you are using a landing page builder with goal of email subscribers, you can duplicate the page and add the Amazon purchase pixel to it.

DISADVANTAGE: Knowing how to install 2 FB pixels on the same site and the two pixels not interfering with each other. If not 2 pixels, need to know how to duplicate landing pages to add only Amazon purchase pixel to it.

Option C (this is a weird one, may apply for any Amazon sellers)
We take your existing pixel and add the Amazon purchase event to it (merged pixel).
Highly recommended if you're a seller focused on Amazon AND have little to no website traffic because then you bypass the disadvantage below. If you grow website purchases over time, please return here and read the disadvantage.

BENEFIT: All benefits from Option A/B and more, not having to install a 2nd pixel. All website and Amazon purchases can be optimized and reported from the same pixel. This is the most comprehensive option for benefit of the new feature. 

DISADVANTAGE: Adding Amazon purchase events to your existing FB pixel may or may not affect how your FB pixel is seasoned. If you have heavy website traffic and website Purchase events, it's unknown if the Amazon data will dilute your website data and reduce performance of existing campaigns running for website purchases. Some argue that the FB pixel and machine learning is extremely smart segmenting all of the data on the pixel and this disadvantage is non-existent. We'll know over time. For advanced FB advertisers, it has not been reported yet that this negatively affects existing website purchase campaigns but you should run this cautiously and notify me to deactivate Amazon data going to merged pixel if performance from historical campaigns drops after several days. Start with Option A or B and if you see traction then can test Option C for best ROI reporting. 

Other discussion points about choosing Options
If you have the plan to track Amazon purchases, it will continue working for any objectives (Website purchases, etc) in any of the 3 options if you are using your default account FB pixel. Activating this new feature does not impact that.
Your Amazon purchases will be tracked in all 3 options. However, your website purchases and website activity will be trackable as well only in Option B and C when using the new feature. For Option A, website purchases only will be tracked when you choose your default original pixel, while Amazon purchases only will be tracked when you choose your new Amazon pixel.


Which pixel?
You should see a new option now that's called "Purchase" but under it says "Amazon purchase pixel" instead of the name of your default pixels. You see this at the Ad Set level when you change the conversion event location for website. You can create draft campaign or edit any current ad to see it then discard changes. You can also customize column and go to metrics under Settings -> Tracking -> Facebook Pixel -> to be able to see the name of the FB pixel that is active at the Ad level. Or edit ad at the Ad level and in the Tracking section below the creative fields will see which Pixel is active.