How do I add adwords conversion tracking code to the 'thank you' page of my form?

You can use the <noscript> code from google adwords.

Once you have copied the <noscript> code you can now embed it to your thank you page. Just copy what is highlighted in yellow on the sample image above and paste it in your HTML settings in your thank you page.

Every time I try this process it disappears when I check if the code is there. How can I confirm it worked?

Hi,

I'm afraid this won't work. Sorry to say but as far as I know noscript or any script codes are not allowed in the custom thank you message. We do not support it for security reasons. The best thing you can do is to use custom thank you URL. Enter the page URL where you have embedded your tracking code. You have to created your custom thank you page and embed your tracking code there.

Thank you so much!