ar10west

Hello,
Please allow me to preface by saying: I have read & understand ALL documentation presented by Squarespace regarding how to implement Google Analytics and the potential discrepancies one might encounter. I have no problem implementing universal Analytics tracking code or Google Tag Manager - I have tried both - both fail at what I am trying to accomplish. That is, reliably parsing eComm sales metrics to Google Analytics. I have yet to find a way to accomplish this simple mission.
Currently, I have reverted back to simple GA tracking code in the provided location. On any given day, for example, our store will have 6 sales, yet only 2-3 are pushed to Google Analytics as an eComm goal - sometimes none. 
As a work-around, I created two Goals in Google Analytics, based upon two distinct url paths related to the order confirmation process, those being:
/checkout/subscription-confirmed/ /checkout/order-confirmed/ Doing so, I was able to capture most of the sales - still not all. So, now I am wondering if there is yet another url path I am not aware of?
We desperately need import sales having source/medium =  CPC to our Adwords campaign in order to gauge performance.
Squarespace support keeps pointing me to articles on the site - which are not helpful.
Using Tag Assistant and recordings, I was able to determine that Squarespace is using two different tracking libraries for Analytics, for example, universal and gtag. I think this is the culprit, but how does one convince their devs to have a look at it?
Has anyone been able to successfully capture ALL sales in Google Analytics? If so, can you please share how you managed to accomplish this task?
Thanks!