Apple Watch SE unable to send SMS to non-Apple devices

My daughter has a new Apple Watch SE. It's paired to my watch but she has her own number/e-sim.

She can send and receive messages via iMessage to other apple devices but she can't send or receive old school SMS messages to non apple devices. She gets a not delivered red exclamation mark.

Calls to both apple and non apple devices are work just fine.

Any ideas?