When you log in using your business email, you will be able to see the notice on top of your inbox like below:
2. To keep using Google Workspace for free, you must self-identify your legacy subscription is for personal use. Simply click on the 'choose now option.'
3. Choose transition path -> 'Personal Use: Stay on no cost Legacy G Suite'
4. You have to confirm the transition to 'no-cost Google Suite services'
5. After giving confirmation of using it for personal use, you successfully opt-in for the free legacy version of G Suite. You don't have to pay Google for using your business email.
6.  Take advantage of a 'G Suite Legacy Free Edition'. This will give you access to all the features of G Suite, including business email and online storage. As it's a free version, you will not able to use premium features of the G suite like support, extra storage, etc. If you really need them in the future then you can easily transition to the paid version.
7. When you log in to your dashboard Google will suggest you upgrade to premium features but it totally depends on your choice.