Whenever i type a number on imessage, it keeps saying “This is number is not registred in imessage. What does it mean? I cant message anyone else
Whenever i type a number on imessage, it keeps saying “This is number is not registred in imessage. What does it mean? I cant message anyone else. 
Solution 1:
How certain are you that the person you are trying to Message actually has an Apple device to receive with [and is correctly signed in with iMessage]?
iMessage is Apple to Apple only. If you try to send from an iPhone to a non-Apple user, the phone will send by SMS instead & the message will appear in green instead of blue. If you're on an iPad without an associated phone number, then it cannot send to SMS.