golang slack send notification with attashed file : I want to send slack notification with attashed file, this is my curent code :

    package Message
    
    import (
        "fmt"
        "os"
        "github.com/ashwanthkumar/slack-go-webhook"
        )
    
    
    func Message(message string, cannalul string, attash bool) {
    
        f, err := os.Open(filename)
        if err != nil {
          return false
        }
        defer f.Close()
    
        _  = f
    
        fullName := "myServer"
        webhookUrl := "https://hooks.slack.com/services/......."
    
        attachment1 := slack.Attachment {}
        //attachment1.AddField(slack.Field { Title: "easySmtp", Value: "EasySmtp" }).AddField(slack.Field { Title: "Status", Value: "Completed" })
        if attash {
            attachment1.AddField(slack.Field { Title: "easySmtp", Value: fullName})
        }
        payload := slack.Payload {
          Text: message,
          Username: "worker",
          Channel: cannalul,
          IconEmoji: ":grin:",
          Attachments: []slack.Attachment{attachment1},
        }
        err := slack.Send(webhookUrl, "", payload)
        if len(err) > 0 {
          fmt.Printf("error: %s\n", err)
        }
    }

My actual code works, but i dont know how i cand add attashed file in my curent code, how i can do this ?