Pinata Pinning A Directory In Golang - go

Question

I am using Pinata to upload files in Go to a private gateway using its submarine feature; while it works well, I am wondering how to pin a directory instead. The documentation says it is "identically to pinning a file, with the main difference being an array of files and need to provide a relative file path for each file in the directory". How can I tweak my current Go code to work for a directory.
package ipfs
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"mime/multipart"
"net/http"
"os"
"path/filepath"
)
func PinFile(filePath string, fileName string) {
//set pinata url for file pinning
url := "https://managed.mypinata.cloud/api/v1/content"
//init method and payload
method := "POST"
payload := &bytes.Buffer{}
writer := multipart.NewWriter(payload)
file, errFile1 := os.Open(filePath)
defer file.Close()
part1, errFile1 := writer.CreateFormFile("files", filepath.Base(filePath))
_, errFile1 = io.Copy(part1, file)
if errFile1 != nil {
fmt.Println(errFile1)
return
}
//set additional pinata option
_ = writer.WriteField("name", "fileName")
_ = writer.WriteField("metadata", "{\"keyvalues\": { \"app\": \"...\" }}")
_ = writer.WriteField("wrapWithDirectory", "false")
_ = writer.WriteField("pinToIPFS", "false")
//close writer if error
err := writer.Close()
if err != nil {
fmt.Println(err)
return
}
client := &http.Client{}
//set new request
req, err := http.NewRequest(method, url, payload)
if err != nil {
fmt.Println(err)
return
}
// set Submarine Key
req.Header.Add("x-api-key", env.GetEnv["SUBMARINE_KEY"])
//add content type to request header
req.Header.Set("Content-Type", writer.FormDataContentType())
res, err := client.Do(req)
if err != nil {
fmt.Println(err)
return
}
defer res.Body.Close()
body, err := ioutil.ReadAll(res.Body)
if err != nil {
fmt.Println(err)
return
}
fmt.Println(string(body))
}