tRPC Procedure Undefined or Not Found

1. Procedure defined in subrouter but not merged into main router
2. Client type generation not updated after adding new procedures
3. tRPC client initialized with wrong URL or missing API base path
4. Procedure naming mismatch between server definition and client call
5. Missing merge or middleware in router causing nested routes to not resolve

Merge routers: In main router file, use router.merge() to include subrouters:
export const appRouter = router({
users: usersRouter,
posts: postsRouter
})

Generate types: Run npm run build or configure ts-build to generate fresh types after procedure changes.

Initialize client: Create tRPC client with correct base URL matching your API route: new TRPCClient({ url: '/api/trpc' })

Verify procedure syntax: Ensure procedure is called as nested path: trpc.users.getProfile.query() matching router structure.