url := "slack://token-a/token-b/token-c"
  err := shoutrrr.Send(url, "Hello world (or slack channel) !")

  url := "slack://token-a/token-b/token-c"
  sender, err := shoutrrr.CreateSender(url)
  sender.Send("Hello world (or slack channel) !", map[string]string { /* ... */ })

  urls := []string {
    "slack://token-a/token-b/token-c"
    "discord://token@channel"
  }
  sender, err := shoutrrr.CreateSender(urls...)
  sender.Send("Hello world (or slack channel) !", map[string]string { /* ... */ })