I cannot activate my iMessages because my phone number doesn't show up in the Settings at Messages Setting > Send & Receive.
Only my email available as choices, there's no phone number shown up.
iPhone X, iOS 12
Watch this GIF to know how to add the Phone Number
Set up your phone number
On your iPhone:
On your other devices, you can now turn on the phone number that you just set up:
If you use this feature and share your Apple ID with someone, you can't prevent them from seeing your conversations. Instead of using the same Apple ID as someone else, set up Family Sharing.
Add or remove your phone number in Messages or FaceTime - Apple ...
Watch this GIF to know how to add the Phone Number
Set up your phone number
On your iPhone:
On your other devices, you can now turn on the phone number that you just set up:
If you use this feature and share your Apple ID with someone, you can't prevent them from seeing your conversations. Instead of using the same Apple ID as someone else, set up Family Sharing.
Add or remove your phone number in Messages or FaceTime - Apple ...
I already add my phone number like that steps in the GIF image for like yesterday, and today still doesn't show up.
My Phone number doesn't show in Send & Receive > Messages Setting
