Maintaining source info across visit to external page during session
I hope someone can help me with this.
I have a store site, and I am using the current analytics.js code. My store is HTTPS throughout and is all on a single domain.
Every page on the site has the tracking snippet, and the Analytics stats show everything fine (except as noted below).
When a customer makes a purchase, he is directed to the payment gateway's payment page. On this page, the customer enters credit card info and agreed to the purchase. The transaction is then processed and the customer is redirected to the "successful sale" page on my site. On this page, I have the ecommerce snippet.
Now, transactions are being successfully recorded, including the data that I specify in the ecommercce snippet. Great. The only problem is, the Source of every transaction shows as the URL of my payment gateway's payment page. In other words, in the reports, tracking is successfully maintained in all cases except when there is a transaction. If the user doesn't make (or attempt) a transaction, the report shows the external source by whence the user entered my site. But if the user attempts a purchase, the temporary excursion to the payment page hosted on the payment gateway provider's domain apparently causes the source data to be reset, thus rendering most potentially useful info about transactions, profitability of different sources, etc, to be absent.
What can I do to make Analytics preserve the contents of the session across the visit to the payment gateway's domain and th return to my own domain?