How to intall whatsapp plus
These happens sometimes. But after 1 or 2 try it will work. 
Try these steps. 

Make Sure you have perfectly running whatsapp installed with your important chat 

1) Go to /sdcard/whatsapp/databases/
Delete all files using FILE MANAGER.
In Whatsapp Go to Settings>Chat settings>Backup Conversations to Backup your conversations ...

2) Uninstall OLDER WHATSAPP 

3) Install Given WhatsApp+'s apk ...

4) Open it &amp; Click AGREE &amp; CONTINUE &amp; enter your number

5) If you have done above steps well then there should be RESTORE BUTTON , Press it
(If you Dont get restore button or you get message like "Your app is not official Download from play store" 
then
uninstall current whatsapp+ &amp; install original whatsapp from play store , do verification process and then chat with 1-2 person again backup chats and then uninstall original whatsapp &amp; install given WhatsApp+ You will get RESTORE button) 

6) Wait ...it might take some long... Press Continue after it finishes