Various Flatpeak API endpoints require you to use device identifiers. These represent a physical or virtual device in your systems. To create a device identifier, use the create-device endpoint. For cross-reference, we recommend that you populate the reference_id field with the unique ID of that device as used in your systems. 
curl --request POST \
  --url https://api.flatpeak.com/devices \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "reference_id": "DEV1234567890"
}'
Store Flatpeak device_id from the response in your systems as a cross-reference to your internal device identifier, in this example, DEV1234567890.