In order to add Google Ads Conversion Tracking to an Instapage landing page, you will have to create a “Thank you” page, which will act as a conversion page. If you chose a premade layout to create your page, check out the layout gallery, as most have a similar “Thank you” page already designed.
Afterward, you will have to link the conversion page to the form on your landing page. Here is a quick guide to help you: https://d.pr/nF84Or.
After you have created and linked the conversion page to the landing page, these are the steps to follow:
1. Place the Google tag in Settings - JavaScript - Head. In Google's documentation here: https://d.pr/HkRS3p, you can find the details regarding the Google tag.
2. In Settings - JavaScript - Body section, paste the Google Ads conversion tracking tag. If you haven't created your tag, follow these instructions: https://d.pr/QU5SG4 to create it;
3. Save the changes, then update your page, and that's it.
All of these operations must be done on the Thank You page, not the original landing page. The code being present on the Thank You page will record visits made to it, which means someone converted from the original landing page.