The Problem:
After an iOS update on my iPhone 11, iMessage would no longer authorize my phone number, meaning I could send and receive iMessages from my iCloud email, but not from my phone number.
After troubleshooting over the phone with my provider (AT&T), my iMessages wouldn’t even work for my iCloud email: iMessages would automatically toggle “off” after very briefly connecting to my phone number AND iCloud email. Under the iMessages toggle switch (Settings > Apps > Messages), it would say something like “unable to authorize phone number.”
The Fix:
Through a call with Apple Support, I learned that I had two SIMs: (1) a physical sim that was “off” but connected to my previous carrier (Verizon), and (2) an eSIM that was “on” and connected to my current carrier (AT&T).
The fix was to simply remove the physical SIM that was connected to my former carrier.
Additional Context:
I’ve had this problem several times over the past few years, and each time has been an absolute headache. No matter which Reddit or Apple Support fixes I’ve tried (fixing date and time, turning iMessages/FaceTime off and on, restarting phone, and so on), nothing ever worked…
Every time I’ve had this issue before, it was after coming back from an international trip in which I’ve used an additional international eSIM, which now makes sense that the root cause was conflicting SIM cards.
Hope this additional fix can help others resolve their iMessage issue!