Ever since cookie variable was introduced, obtaining clientId became pretty easy . In this method, we will use the Cookie Variable in GTM. ( old post for extracting clientId with CutsomJs)
So, let’s start with the basics that, the “_ga” is the name of GA cookie that stores the client id.
now we will go ahead and create a new variable of type “1st Party Cookie” and at variable part give the name of cookie – “_ga”. This variable will extract the value of the cookie with name “_ga” .
Now, as usual, debugging / previewing the job.