Insert code into the < head > section using Google Tag Manager (GTM).
Here is the procedure:
1. Log in to your Google Tag Manager account at https://tagmanager.google.com/.
2. Select the container in which you want to add the code to < head >. If you don't have a container created, create one by clicking the "Create Account" button and follow the instructions.
3. After selecting a container, click on the container name to open the main GTM interface.
4. Click on "Tags" in the navigation bar on the left.
5. Click on the "New" button and select the "HTML" tag type.
6. In the tag settings, go to "Constants".
8. Once the code has been entered, click on the "Back" button on the top left of the screen.
9. Click the "Submit" button in the top right corner of the screen to save the change.
10. Now you have to publish the changes. Click on the "Publish" button in the top right corner of the screen.
11. A preview of the changes dialog box pops up. Click the "Publish" button to actually save the changes.
12. Finally, you have to paste the GTM code on your website. Copy the GTM container code, which is located at the top of the GTM interface (at the container level, not at the tag level).
After these steps, the code you put into GTM should be correctly inserted into the < head > section of your website.
Make sure that you are testing and verifying that you are implementing the code correctly in GTM and that the code is working correctly on your website.