API Return types?

Hey Klaviyo team, 

I am wondering where I can find the return types for specific API queries? For instance I have the following “Create Client Subscription” operation, but I am manually typing out the return types:

interface CreateClientSubscription {
  email?: string | null;
  phone?: string | null;
  status: number;
  message: string;
  error: string | null;
  submittedAt: string;
}

/**
 * Subscribes a user to a specified email list.
 * @param email - The user's email address
 * @param listId - The email list ID (newsletter)
 * @returns A Promise resolving to the subscription data
 * @see https://developers.klaviyo.com/en/reference/create_client_subscription
 */
const newsletter = async (
  email: string,
  listId: string
): Promise<CreateClientSubscription> => {
  return await $fetch('/api/klaviyo', {
    method: 'POST',
    body: {
      data: {
        type: 'subscription',
        attributes: {
          profile: {
            data: {
              type: 'profile',
              attributes: { email }
            }
          }
        },
        relationships: {
          list: {
            data: {
              type: 'list',
              id: listId
            }
          }
        }
      }
    }
  });
};

Ideally, it would be best to just import the pre-defined types into my Klaviyo operations. I am using codegen, but I dont think this can be done. Perhaps there is another repo/library I am missing?

Thanks!:)