I have set up the Family Sharing by using a parent account with a real Apple ID and added a child account with also a real Apple ID as a member under the same family group with the parent account. Then, I download our app from the Apple app store for testing the Ask-To-Buy feature in the Production environment.
When I use the child account to purchase an auto-renewable subscription product within the app, it pops a dialog box asking me to ask for permission. Then, I send a request to the parent account to ask for the permission and I use the parent account to approve the purchase. After that, it pops up the error message of "Your Purchase Could Not Be Completed" and the purchase is failed.
On the same device, if I straight away use the parent account to purchase the auto-renewable subscription product within the same app, then the purchase will be completed successfully. However, I cannot complete the purchase through the Ask-To-Buy feature by using the child account under the same family group with the parent account.