How to add subscription box within posts

I have a jetpack subscriptions box on the front page of my website, but I’m wondering how I can add a subscription button inside all my posts. Just so when people read a blog article, they can click subscription at the bottom.

Does anybody know how to do this? It doesn’t have to be with jetpack. If you know of other plugins that will work I’d appreciate the help.

Here’s the website in question:

https://prosperitasassetmanagement.com/