There are a few ways, but I believe SSOT (single source of truth) is key, as others basically said. Some ways:

1. Shared TypeScript types

2. tRPC/ts-rest style: Automagic client w/ compile+runtime type safety

3. RTK (redux toolkit) query style: codegen'd frontend client

I personally I prefer #3 for its explicitness - you can actually review the code it generates for a new/changed endpoint. It does come w/ downside of more code + as codebase gets larger you start to need a cache to not regenerate the entire API every little change.

Overall, I find the explicit approach to be worth it, because, in my experience, it saves days/weeks of eng hours later on in large production codebases in terms of not chasing down server/client validation quirks.