Google Tag Manager

I have developed a booking app for a hair transplant clinic so that clients can book video assessments via their website. The app is embedded in their website via an iFrame.

Their web development team want to be able to track their goals and conversions via Google Tag Manager and Google Analytics. They can easily track the number of clients visiting the booking page but need to be able to identify which of these then book an assessment. Could you give me any guidance on how to integrate Google Tag Manager into my BF app?

I have the same question - just can’t figure out how to do this step:

“Additionally, paste this code immediately after the opening tag:”

I can see how to add tags into the DOM, but not “body”.