If you can't join chatting groups may be caused by the following reasons:

1. If you have already sent join application and waiting for the approval, we suggest you be patient and wait for your admin agree, then you can join the group;
2. If your group is Secured Enterprise group/All-hands Group/Department Group, please make sure you are in the right enterprise, otherwise, you cannot join the group (you can contact the enterprise admin to add you into the organization);
3. If you are in the enterprise already, but you can't join the group by scan QR code, please contact your group admin to check is your QR code right or not;
4. When you scan the QR code, please use DingTalk mobile app, not other apps.  
If you are looking for "can't join organization/ enterprise, please click Can't join enterprisefind the reason

Tips:
Admin go to [DingTalk mobile app] - [Contacts] - [Settings] - [Add employees to the team]; Or go to desktop Admin Panel: （oa.dingtalk.com）- [Contacts] - [Invite Members].