Google API Contacts v.3, PHP: add a contact to the group

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I successfully managed to create a new contact with cURL, but when I want to add group membership for this contact, I get 400 error. I've read this docsand made the same request, but it didn't work. What am I doing wrong? Thanks for any ideas!This is how I create an XML with group information:\[code\]$doc = new DOMDocument('1.0', 'UTF-8');$doc->formatOutput = true;$entry = $doc->createElement('entry');$entry->setAttribute('gd:etag', $etag);$doc->appendChild($entry);$category = $doc->createElement('category');$category->setAttribute('scheme', 'http://schemas.google.com/g/2005#kind');$category->setAttribute('term', 'http://schemas.google.com/contact/2008#contact');$entry->appendChild($category);$id = $doc->createElement('id', 'http://www.google.com/m8/feeds/contacts/default/base/'.$idgmail);$entry->appendChild($id);$updated = $doc->createElement('updated', $update_info);$entry->appendChild($updated);// Add group info (My Contacts)$group = $doc->createElement('gContact:groupMembershipInfo');$entry->appendChild($group);$group->setAttribute('deleted', 'false');$group->setAttribute('href', 'http://www.google.com/m8/feeds/groups/default/base/6');// Add another group info$group = $doc->createElement('gContact:groupMembershipInfo');$entry->appendChild($group);$group->setAttribute('deleted', 'false');$group->setAttribute('href', 'http://www.google.com/m8/feeds/groups/default/base/'.$my_group_id);$group_info = $doc->saveXML();\[/code\]And this is my cURL:\[code\]$url = 'https://www.google.com/m8/feeds/contacts/default/full/'.$idgmail.'/';$headers = array('Host: www.google.com','Gdata-version: 3.0','Content-length: '.strlen($group_info),'Content-type: application/atom+xml','If-Match: *','Authorization: OAuth '.$access,);$curl = curl_init();curl_setopt($curl, CURLOPT_URL, $url);curl_setopt($curl, CURLOPT_CUSTOMREQUEST, "POST");curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);curl_setopt($curl, CURLOPT_POSTFIELDS, $group_info);curl_setopt($curl, CURLOPT_FAILONERROR, true);$resp = curl_exec($curl); print_r($resp); // Prints nothingecho curl_getinfo($curl, CURLINFO_HTTP_CODE); // Gives 400curl_close($curl);\[/code\]