Invoice with Future GL Date and Invoice Date in Past and Cannot change Complete to Incomplete

Good day,

I have a client who has created an invoice for a customer with a GL Date in the Future and the Invoice date in a past period.  The invoice cannot be changed back to Incomplete.  There was an error in the amount to be billed and they cannot adjust or apply a credit to the invoice.  In attempting the credit the system says it cannot due to Future Date.

I've suggest they create a credit memo with the same FUture Date as the invoice and when the Future is now present, then they should be able to offset.