Api design, communication between microservices

I am writing an app which simply has 3 microservices.

1. Basket which holds basket and items

class Basket {
  Long id;
  List<Items> items;
}

class Item {
  Long id;
  String name;
  Long pricingId;
}

2. Pricing which calculates and holds price for item

class Pricing {
  Long id;
  BigDecimal value;
}

3. Calculation which calculates and holds sum for basket

class Calculation{
  Long id;
  BigDecimal sum;
}

For communication i use synchronous requests via REST.

What is the best way to design api between microservices.

ie. how should i fetch just Calculation with only basket id

I use vanila JS on the front side.