Channel flow tag for the server GTM stores the source/medium of all user's interactions with the site into cookies.  

Cookie names Channel Flow tag uses:

• Channel_flow - records the source/medium flow of all user interactions with the site
• Channel_flow_first - records the first source/medium
• Channel_flow_last - records the last source/medium

URL Source. Select variable that container URL. By default, it uses page_location.

Referrer Source. Select variable that contains Referrer URL. By default, it uses page_refferer. 

Search Engines Regular Expression. Use this field to modify regular expressions that identify organic traffic. 

Cookie lifetime. Set cookie lifetime in seconds. 

Use Cases:

• Track user source/medium flow using server Google Tag Manager