Apple Watch Series 9 cellular service is not working

The checks in more detail

If it does not work, check that the plan is active with the carrier, toggle Airplane Mode on both devices for fifteen seconds, restart both devices and check the Watch app, Cellular. A Series 9 bought in another country may not support your carrier. The watch's eSIM is tied to the plan, and moving to a new iPhone or a new carrier may require re-adding the plan. Cellular use drains the battery faster, so use Low Power Mode on long outings. For emergency calls, the watch can call on cellular without the iPhone. If setup fails with an error, contact the carrier, who can reset the line.

If you travel, remember that the watch's cellular plan may not work abroad, and some carriers offer a travel pass for the watch; otherwise the watch uses Wi-Fi or the iPhone abroad. Use the Watch app, Cellular to see plan details and roaming options. For an emergency, the watch can still place emergency calls on any available network, even without an active plan, which is a safety feature in some countries. Check your carrier's page for the watch plan's fee, since a watch line is usually billed separately, and some carriers limit data or throttle the watch.

If you share a plan with family, the watch line may need to be set up by the account owner. If you change your iPhone number, the watch's number follows the plan, so update the plan in the Watch app. Keep the carrier's customer service number handy for activation problems. Test the cellular connection properly by turning off Wi-Fi on the iPhone and walking away with the watch, or put the iPhone in Airplane Mode while the watch has cellular on, and check that Control Center shows the green Cellular button and that a message or a call goes through. This confirms the plan works before you rely on it for a run without your phone.