This page should be plain and simple, as it will be used as an iframe. For example, here is mine: https://tonydinh.com/subscribe.

The page should has a fully functional subscribe button. You can write your own code (JavaScript!) or steal my ReactJS code here.
Use the /embed command. Like this:
CleanShot 2021-12-10 at 11.12.03.mp4
That's it! Here is the result 👇
https://tonydinh.com/subscribe
Hello there, I'm Tony Dinh.

I quit my high paying job to work on my side projects with a mission to make a living from my apps and live an independent life. 🌴
🏖️ Read my story → https://newsletter.tonydinh.com/
https://tonydinh.com/subscribe
❤️ Thanks for reading!