Go

In Go, we'll be using the net/http standard library to send HTTP requests. Here's how you can use the book search API with Go:

First, make sure you import the necessary libraries at the top of your file:

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
)

Then, you can use the following code to make the API request:

type Book struct {
	Title  string `json:"title"`
	Author string `json:"author"`
}

type Query struct {
	Query string `json:"query"`
}

func searchBook(query string) ([]Book, error) {
	url := "https://api.promptjoy.com/api/mVMCpq"
	var jsonData = []byte(`{"query":"` + query + `"}`)

	req, err := http.NewRequest("POST", url, bytes.NewBuffer(jsonData))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("x-api-key", os.Getenv("PROMPTJOY_API_KEY"))

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	body, _ := ioutil.ReadAll(resp.Body)

	var books []Book
	err = json.Unmarshal(body, &books)
	if err != nil {
		return nil, err
	}

	return books, nil
}

func main() {
	books, err := searchBook("your_search_term")
	if err != nil {
		fmt.Printf("The HTTP request failed with error %s\n", err)
	} else {
		for _, book := range books {
			fmt.Println("Title: " + book.Title + ", Author: " + book.Author)
		}
	}
}

Replace "your_search_term" with the book you're searching for. This function will return a slice of books.

Remember to handle exceptions and errors as needed in your actual application code.

Note: In this example, the API key is retrieved from environment variables for security reasons. Ensure that you've set the PROMPTJOY_API_KEY environment variable in your environment where this code will be executed.