HTML hosting. That is the product.
If your workflow is still “save index.html,” you should not have to adopt a cloud account model made for twelve microservices.
Put index.html at the root
The zip’s top level should contain index.html (or index.htm). Nested junk-in-a-folder is the usual way a first deploy 404s.
Assets
Relative paths work. Absolute paths to your laptop do not. That is the only HTML hosting gotcha that matters.
Questions
Do you support PHP includes?
Not on a static site. If you need server-side includes or PHP, that is a different site type on the same platform — and no longer static hosting.