Your welcome ^^

package main

import (
	"bytes"
	"net/http"
	"sync"
)

func main() {
	client := http.Client{}
	wg := &sync.WaitGroup{}
	for i := 0; i < 100; i++ {
		wg.Add(1)
		go func() {
			bodyReader := bytes.NewReader(
				[]byte(
					`{"content":"#score","recipient_id":303747,"auth":"..............."}`,
				),
			)
			req, err := http.NewRequest(
				"POST",
				"https://lemmy.zip/api/v3/private_message",
				bodyReader,
			)
			if err != nil {
				panic(err)
			}
			req.Header.Set("Accept", "*/*")
			req.Header.Set(
				"User-Agent",
				"Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/116.0",
			)
			req.Header.Set("Accept-Language", "fr-FR,fr;q=0.8,en-US;q=0.5,en;q=0.3")
			req.Header.Set("Accept-Encoding", "gzip, deflate, br")
			req.Header.Set("Content-Type", "application/json")
			req.Header.Set("Referer", "https://lemmy.zip/create_private_message/303747")
			req.Header.Set("Origin", "https://lemmy.zip")
			req.Header.Set("DNT", "1")
			req.Header.Set("Sec-Fetch-Dest", "empty")
			req.Header.Set("Connection", "keep-alive")
			client.Do(req)
			wg.Done()
		}()
	}
	wg.Wait()
}