How to switch phones with G5 mobile?

I'm currently sitting on hold with dexcom, but with how long that usually takes, I figured I might just have more luck posting here.

My son has been using the G5 paired to an iPhone 4s. We recently switched carriers and got a new iPhone. However when I go to pair the transmitter to the new phone I get an error that says "We are experiencing a temporary issue with the dexcom servers. Please try again later."

Tried giving it a day but same message. Tried turning the old phone off, but same message. Do I need to unpair the transmitter from the old phone somehow? I'm sure I'm not the first person to get a new phone, but Google has nothing. Thanks in advance.

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