Cannot activate an eSim on an Apple Watch from AT&T FirstNet

Cannot activate an eSim on an Apple Watch from AT&T FirstNet

• I've tried everything, including sending the Watch in for Apple repair twice.
• During the initial Apple Watch setup wizard, the Cellular step is unavailable:
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• When continuing, going to Settings ➜ Cellular just shows Not Available.
• I've tried (on AT&T site) recreating the eSim (failure).
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