How to set the product ID in the Google Inappproducts:insert API

Question

The Google REST API for in-app purchases describes the payload structure to be used when inserting (creating) a new product (see below).

I don't see where I set the Product ID here for the REST API call.

What am I missing?

This is how the Product ID is set when manually creating the product in the Google Play Console:

And this is the API payload spec:

{
  "packageName": string,
  "sku": string,
  "status": enum (Status),
  "purchaseType": enum (PurchaseType),
  "defaultPrice": {
    object (Price)
  },
  "prices": {
    string: {
      object (Price)
    },
    ...
  },
  "listings": {
    string: {
      object (InAppProductListing)
    },
    ...
  },
  "defaultLanguage": string,
  "subscriptionPeriod": string,
  "trialPeriod": string,
  "gracePeriod": string,

  // Union field TaxAndComplianceType can be only one of the following:
  "subscriptionTaxesAndComplianceSettings": {
    object (SubscriptionTaxAndComplianceSettings)
  },
  "managedProductTaxesAndComplianceSettings": {
    object (ManagedProductTaxAndComplianceSettings)
  }
  // End of list of possible types for union field TaxAndComplianceType.
}