When GEO header power-up is enabled, the following headers are added to the Incoming HTTP Request inside the sGTM:

• X-GEO-Country
• X-GEO-Region
• X-GEO-City

To use these Requests Headers in the server Google Tag Manager create a new variable with the variable type Request Header and type Header Name. 

By activating the GEO Headers power-up, you gain valuable information about the location of your website visitors. With the help of this data, you can modify tag delivery based on the user's country, region, or city. For example, ask user consent based on the country where a user is located or build remarketing audience depending on their territory.