To edit the upcoming invoice amount for a user e.g. to apply a discount or add a purchase made in the gym, follow the steps below.
Navigate to Finance > Subscriptions.
Select the user you wish to edit to view their subscription. Select the pencil against the upcoming invoice to edit the amount.
Change the amount and select Update.
The next invoice amount is updated.
Note: This method only updates the next invoice, once the next invoice is paid, any subsequent invoices will revert to the price on the subscription.