Attempting to share glucose sensor data across country borders, via the Dexcom Follow app, yields an opaque error message to the recipient: "This invitation expired or was already used. Ask your Sharer to invite you again."

From https://www.reddit.com/r/dexcom/comments/1dhxnv9/comment/l90jytv/

  "The CGM and Follow app have to both point to the same server region. The CGM data is stored in one of three regions, depending on where you live. USA customers have their data stored in the USA, Japanese and Singaporean customers have their data stored in Japan. Everybody else has their data stored in the EU, which should include Australia.. That’s why the invitation fails — it only exists in the region with your data."

The Dexcom sensor data collector app requires device geo-location permission when the app is installed, which is used to set country language and apparently the sensor data storage location.

The Dexcom Follow app appears to be using the device's app store country code as access control for sensor health data, which makes it impossible to share sensor data between US and non-US customers.

Is this data separation a regulatory requirement of some countries?