Spring Webflux How to do call 2 different services sequentially without blocking?

I am having an issue with webflux

let me describe what I want to do synchronously.

First, I want to save a product to the db and get a generated ID

Next I want to save reviews of the product with productId.

I want to do this in one service call to the microservice controller. I do not see how this can be accomplished in controller without blocking (which I know is something I should not do)

I am sending data like the following to my restcontroller

{
  name: "product 1",
  weight: 5,
  reviews: [
  {
      rating: 5,
      post: "review post"
  }, {
     rating: 10,
     post: "Second review post"
  }]
}

public class MyService {
  //This will call another micro-service and returns a Mono with the saved product
  public Mono<Product> saveProduct(Product product) { ... }

  //This will call another micro-service to save the review
  public Mono<Void> saveReview(Review review) { ... }
}

@RestController
public class MyController {

@Autowired
MyService service;

@PostMapping("/composite-product")
public Mono<Void> saveCompositeProduct(CompositeProduct cp) {
  // The id is null at this time
  Product product = new Product(cp.getName(), cp.getWeight());
 
  return service.saveProduct(product)
    .flatMapMany(savedProduct -> {
       if(cp.getReviews() == null) return Flux.empty();
       
       // I add the product id to the review
       List<Review> reviews = cp.getReviews().stream()
         .map(review -> new Review(savedProduct.getId(), review.getRating(), review.getPost())
         .collect(Collectors.toList());

      // I try to save the reviews but it does not work because nothing ever 
      //subscribes to it. I do not want to add any type of subscribe method
      // or block method which I know is wrong to have in a webflux application
       return Flux.fromIterable(reviews)
         .map(r -> service.saveReview(r));
    }).then();
}

How can I make this work?

Use flatMap instead of map operator. flatMap subscribes to Mono internally just like flatMapMany does to Flux.

return Flux.fromIterable(reviews)
           .flatMap(r -> service.saveReview(r));