Check that iMessage is on and both devices use the same Apple Account in Messages. If both already use Messages in iCloud, forwarding is built in. Otherwise, on the iPhone open Settings → Apps → Messages → Text Message Forwarding and turn on your Mac.
01Check which device misses the text
Section linkAsk someone to send a fresh carrier text to your iPhone, rather than testing with an iMessage. If it never arrives on the iPhone, fix delivery to the phone first. If it arrives there but not on the Mac, check the forwarding setup and keep the iPhone on and connected to Wi-Fi or a cellular network for the test.
02If the forwarding option itself is missing
Section linkIf both devices use Messages in iCloud, check whether the new text appears on the Mac before changing anything; separate forwarding setup is unnecessary. If you need the separate toggle and it is missing, Apple says to turn iMessage off and back on on the iPhone, then tap Send & Receive and sign in again.
03If Text Message Forwarding opens but the Mac is absent
Section linkOn the Mac, open Messages → Settings → iMessage and check the signed-in Apple Account. On the iPhone, compare it with the account under Messages → Send & Receive. Sign in with the matching account if needed, return to Text Message Forwarding, and turn on the Mac when it appears. Have the sender try a fresh carrier text again.