You may need your Client ID when setting up an integration with your MMP / Attribution Partner. It may also be called Organization ID depending on the MMP you use.
To find it in your SearchAdsHQ account, navigate to Integrations on the left-hand menu. Hover your mouse pointer over one of the MMP logos until you see View Settings button.
Click on VIEW SETTINGS. A pop-up window will open. You can copy your Client ID from there.