Check if Messages is turned on in Settings
Open Settings
Tap your Apple ID name
Tap iCloud
Turn on Messages if it is off
Make sure iMessage is enabled
Open Settings
Tap Messages
Turn on iMessage
Check your internet connection
Restart your iPhone
Sign out of Apple ID and sign back in
Open Settings
Tap your Apple ID name
Scroll down and tap Sign Out
Sign back in with your Apple ID
Update your iPhone to the latest iOS version
Open Settings
Tap General
Tap Software Update
Restore messages from an iCloud backup
Open Settings
Tap General
Tap Transfer or Reset iPhone
Tap Erase All Content and Settings
Set up your iPhone and choose Restore from iCloud Backup
Restore messages from a computer backup
Connect iPhone to your computer
Open Finder or iTunes
Select your iPhone
Choose Restore Backup
Check the Recently Deleted folder in Messages if available
Open Messages
Tap Edit or Filters
Tap Recently Deleted
Recover deleted messages if they are there
Contact your carrier if SMS messages are missing
Contact Apple Support if messages still do not return