There are two versions of integrating Google analytics (GA) with ecommerce provider.
1. Classic
2. Universal Analytics
The URL below provides details of how to implement using classic analytics:
https://support.fastspring.com/hc/en-usis
An attempt is made to integrate FastSpring with Google Analytics (this is an older version and not sure if it works):
https://support.fastspring.com/hc/en-us/articles/207439096-Integrating-Google-Universal-Analytics-with-FastSpring
The second method uses Universal Analytics and this is what google recommends for implementation.
The following uses tag manager:
https://support.fastspring.com/hc/en-us/articles/2074390https://support.fastspring.com/hc/en-us/articles/207439096-Integrating-Google-Universal-Analytics-with-FastSpring96-Integrating-Google-Universal-Analytics-with-FastSpring
https://support.fastspring.com/hc/en-us/articles/207439096-Integrating-Google-Universal-Analytics-with-FastSpring
Implementing Google Tag Manager with FastSpring:
https://support.fastspring.com/hc/en-us/articles/207439086-Implementing-Google-Tag-Manager-with-FastSpring
https://support.fastspring.com/hc/en-us/articles/207439016-Directing-Link-Source-Traffic-source-X-to-your-Website
*** Check this comprehensive guide:
https://docs.fastspring.com/integrations/extensions-tab/google-universal-analytics