iMessage not working
Why is my iMessage saying waiting to activate
Question marked as
If you can’t turn on or sign in to iMessage or FaceTime, read this support article --> If you can’t turn on or sign in to iMessage or FaceTime - Apple Support
Also try restarting your device. That cleared up an activation issue we had, and it doesn't hurt to try.
If it still isn't working after a day, do as the article instructs and contact Apple --> Contact - Official Apple Support