To add pagination in single post

You do not need any plugin for this. Do this instead:

1. Login to admin
2. Open your post in Editor and then switch to Text mode
3. Insert <!--nextpage--> where you want to create page break. You can add it as many time you want in your post body in different placed.
3. Update your post.

The above action will create a pagination at the bottom of your post like the screenshot here: https://prnt.sc/geuxba

That should be it! Let me how it goes!