in the Migrate private metafields docs, the App-owned metafields section contains inconsistent and incorrect data.
it states that the app owned metafield needs to be under these 2 structures:
app-{your-app-id}--{some-namespace}
app-12345–client_name
(notice double dash merged)
while both are incorrect, there should be a double dash between each component as stated in
About reserved prefixes doc section Create a metafield definition under a reserved namespace
the correct syntax is:
app--{your-app-id}--{some-namespace}