Open the Settings app on your iPhone or iPad.
Scroll down and tap on your Apple ID, which is usually your name and picture at the top of the screen.
In the Apple ID menu, scroll down and tap on "Contact Key Verification," located near the bottom of the menu.
Inside the Contact Key Verification settings, you'll see a switch next to "Verification in iMessage."
Tap on this switch to enable Contact Key Verification for iMessage.
Once enabled, you may be prompted to enter your Apple ID password or use Face ID/Touch ID to confirm the changes.
After confirming, you'll see a message indicating that Contact Key Verification is now active for iMessage.
You can now exit the Settings app, and Contact Key Verification will be in effect for iMessage conversations. (Image Credit: All Images From Freepik)