Transparent image background become white after posting on facebook page by Graph-APi (Javascript)

问题

Strangely my transparent image background become white after posting it on facebook page through graph api. This is my original image which has transparent background:

But after posting it on facebook I am getting this one which has white background:

For getting the original image link, I am checking the height and width of the image object from response and then just getting the source from it.

    FB.api(
      '/'+photoID,
      'GET',
      {"fields":"images"},
      function(response) {
        if (!response || response.error) {
          reject(response.error);
        } else {
          var imageArray = response.images;
          imageArray.forEach((item) => {
            console.log(item.width);
            if (item.width == imageWidth && item.height == imageHeight) {
              resolve(item.source);
            }
          });
        }
      }
    );

This is the full code for posting image on facebook:

function postImageOnFacebookPageAndGetPhotoID(url) {
  return new Promise(function(resolve, reject) {
    FB.api(
      '/'+pageID+'/photos',
      'POST',
      {"url":url, "access_token":document.getElementById("pageAccessToken").value},
      function(response) {
        if (!response || response.error) {
          reject(response.error);
        } else {
          resolve(response.id);
        }
      }
    );
  });
}

function getOriginalUploadedImageURL(photoID, imageWidth, imageHeight) {
  return new Promise(function(resolve, reject) {
    FB.api(
      '/'+photoID,
      'GET',
      {"fields":"images"},
      function(response) {
        if (!response || response.error) {
          reject(response.error);
        } else {
          var imageArray = response.images;
          imageArray.forEach((item) => {
            console.log(item.width);
            if (item.width == imageWidth && item.height == imageHeight) {
              resolve(item.source);
            }
          });
        }
      }
    );
  });
}

And this is how I am calling it:

postImageOnFacebookPageAndGetPhotoID(categoryIconUrl).then(
  function(result) {
    if (result) {
      //Get the original image by photoID with the help of width and height
      //Here result is the photoID
      getOriginalUploadedImageURL(result, "66", "66").then(
        function(result) {
          if (result) {
            //result is the original photo url of the uploaded image
            console.log(result);
          }
        }).
        catch(
          function(error) {
            alert(error);
          }
        )
    }
  }).
  catch(
    function(error) {
      alert(error);
    }
  )  

I need original transparent background image. What am I missing here?
Thanks!

来源：https://stackoverflow.com/questions/63306230/transparent-image-background-become-white-after-posting-on-facebook-page-by-grap