Documentation of GAM Click  Macro: https://support.google.com/adxbuyer/answer/3187721?hl=en

NOTE: If no other instructions are given we will insert the %ICK_URL_UNESC%% macro described in the GAM documentation linked above.

For us to be able to track click count in GAM we need to be able to insert a click macro into the script tag. We would like you to always deliver thescript with a placeholder for where to insert our click macro with the following format: `click="[Google_Click_Macro_Here]"`.The name of the variable, `click=`, is not important to us,you can name it whatever you like as long as the placeholder-name is very clear about where to insert the click macro.
Preferably name the placeholder [Google_Click_Macro_Here] as in the example above.

Example Third-Party script:<SCRIPT language='JavaScript1.1' SRC="http://www.3rdpartydomain?key1=value1&key2=value2&cachebuster=[Cachebuster_Macro_Here]&click=[Google_Click_Macro_Here]"></SCRIPT>