It is possible to top-up accounts purchased through Orchid's VPN client app when your balance is running low. To top-up your account:
Select "Manage Accounts"
If needed, select the gear/cog and choose the account you wish to top up
Select "Add Credit"
Choose how much credit you wish to add
Complete the in-app purchase
Once the purchase and transaction are confirmed, the credit will be added to your Orchid account!