To manually implement the Taboola Pixel using Google Tag Manager using custom HTML tag, please follow the instructions below.

How to Install Taboola Pixel using the Google Tag Manager. 

1. Open your Google Tag Manager and select container of your website to go to Workspace.
   
2. Click Add a New Tag in the New Tag box. 
3. Name the tag. For example, "Taboola - Base Code". 
   
4. Click on the Tag Configuration and select the tag type as Custom HTML. 
   
5. Copy & Paste the Taboola Pixel code from Backstage into the HTML box. 
   
6. Click on Advanced Settings dropdown and select Once per Page under Tag firing options. 
   
7. Select All Pages for firing triggering. 
   
8. Save the pixel. 
   
9. Go to the Preview to verify the pixel is added properly
10. Open your website in a new tab and check if your custom HTML has been fired.
11. Click Submit and Publish to save.

How To Track Specific Events 

Easily track event-based user interactions within your web assets. You can use event-based conversions for special (and sometimes more complex) scenarios such as tracking users who read up to a certain length or percentage of the page, clicking a button, or for tracking engagement on a page, where people are not leaving too quickly and are reading the content.

1. Create the relevant conversion event in Backstage.
2. Open your Google Tag Manager and select your website's containers to go to the working space. 
3. Name the tag. 
4. Click on the Tag Configuration and select the tag type as Custom HTML. 
5. Copy the snippet of code from Backstage and Paste it in HTML box.
    
6. Click on Advanced Settings dropdown and select Once per Event under Tag firing options. 
7. Tick the the box of Fire a tag before under Tag Sequencing and select the Taboola Base Code (Note: Base code must fire before your event). We do not recommend implementing any additional sequencing before the Taboola Base Code or Event Code, as that may cause discrepancies and errors in tracking. 
   
8. Select relevant triggering option. If you wish to track clicks, set click trigger. If you wish pixel to be fired when user scroll down to the website, set scroll depth trigger. (Note: Client need to set triggers in advance to trigger such events)
9. Save, submit and publish. 

How to Verify Pixel Implementation

The final step is to verify whether the pixel is added and properly running on your website.

1. Click Preview from the top right of the working space.
   
2. Open your website in a new tab.
3. If you see that your Taboola Pixel has been fired like in the images below, it’s working properly.
   
   
4. Click Submit then Publish to save all changes.
5. Go back into Backstage and see if the window has changed to Pixel is Active (Note: It may take up to 20 minutes for your pixel status to change after installing it).