How do I can post a multiple photos via Facebook API

You can now publish multiple images in a single post to your feed or page:

For each photo in the story, upload it unpublished using the {user-id}/photos endpoint with the argument published=false.

You'll get an ID for each photo you upload like this:

{  "id": "10153677042736789"}

Publish a multi-photo story using the {user-id}/feed endpoint and using the ids returned by uploading a photo

 $response = $facebook->api("/me/feed", 'POST',  array(    'access_token=' => $access_token,    'message' => 'Testing multi-photo post!',    'attached_media[0]' => '{"media_fbid":"1002088839996"}',    'attached_media[1]' => '{"media_fbid":"1002088840149"}'  ));

Source: Publishing a multi-photo story

You can make batch requests as mentioned here: https://stackoverflow.com/a/11025457/1343690

But its simple to loop through your images and publish them directly.

foreach($photos as $photo){       //publish photo}

Edit:

This grouping is done by facebook automatically if some photos are uploaded into the same album.

Currently you cannot create an album in a group via Graph API - it is not supported (as of now), see this bug.

But you can do this - create an album manually, then get the album_id by-
\GET /{group-id}/albums, then use the the code with album_id instead of group_id-

foreach($photos as $photo){   $facebook->api("/{album-id}/photos", "POST", array(      'access_token=' => $access_token,      'name' => 'This is a test message',      'url' => $photo      )   );}

I've tested it, see the result-

Actually you can upload a multi story photo(I did it using Graph Api and PHP) but the problem comes if you need scheduled this post.Your post is schedule but also it shows on the page's feed.

P.S. I'm using Graph Api v2.9

PHP Code

$endpoint = "/".$page_id."/photos";foreach ($multiple_photos as $file_url):array_push($photos, $fb->request('POST',$endpoint,['url' =>$file_url,'published' => FALSE,]));endforeach;$uploaded_photos = $fb->sendBatchRequest($photos,  $page_access_token); foreach ($uploaded_photos as $photo):array_push($data_post['attached_media'], '{"media_fbid":"'.$photo->getDecodedBody()['id'].'"}');endforeach;$data_post['message'] = $linkData['caption'];$data_post['published'] = FALSE;$data_post['scheduled_publish_time'] = $scheduled_publish_time;$response = $fb->sendRequest('POST', "/".$page_id."/feed", $data_post, $page_access_token);$post_id = $cresponse->getGraphNode()['id'];