Syncing messages between devices
To ensure your messages sync correctly between your old and new devices, please follow the steps below.
On the old device:
Perform an iCloud backup
Go to Settings > your name > iCloud
Under Saved to iCloud, make sure Messages is turned on
Go to iCloud Backup and select Back Up Now
On the new device:
Go to Settings > your name > iCloud
Under Saved to iCloud, tap Messages in iCloud
Select Sync Now
For help with any of these, please select the following option.