I’m not sure if anyone else is having this issue, but the button to purchase the Basic site plan is not linked to anything, so I cannot purchase a basic plan. Only the CMS and Business site plans buttons are clickable.
Welcome to the community @Catherine_Lim
It sounds like your project has at least one CMS Collection active:
If you’re not using those features, you can delete the Collection(s) — after unlinking any CMS elements — and you should be able to pay for a Basic site plan.
Feel free to reply with your read-only link if you run into any issues and I can take a peek.