I'm new to this posting business so please be patient.

I have 6 stores set up in magento 1.9 representing the 6 different departments of the charity, they have individual order number prefixes, however what I really need is the ability for the 6 stores to share invoice numbers. Allowing the accounted to see one long list of invoices from all the stores.

When I have tried to set this up however I get conflicts 'invoice can't save' because another store has already used the invoice number. If I have not been clear or if you require more information please ask.

Does any one know of a way to implement this, I would be very grateful