Set up your iPhone for SMS text messages on your Mac
Set up your iPhone so that you can receive and send SMS and MMS text messages on your Mac. Once you’ve set up your iPhone, if you receive an SMS message on your iPhone, it also appears on your Mac. Plus, when you send a message to a friend who uses a phone other than an iPhone, your message is sent as an SMS message instead.
Important: To receive and send SMS and MMS messages on your Mac, your iPhone must have iOS 8.1 or later, and your iPhone and Mac must be signed into iMessage using the same Apple ID. For more information, see the Apple Support article Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch.
On your iPhone, go to Settings > Messages.
Tap Text Message Forwarding.
Tip: If you don’t see Text Message Forwarding, make sure you’re signed in to iMessage using the same Apple ID on both your iPhone and your Mac.
Enable your Mac in the list of devices.
On your Mac, open Messages.
A six-digit activation code appears.
Enter this code on your iPhone, then tap Allow.