Invoice block series not visible during the Invoice process

Reasons for invoice block series not visible during invoice creation:

• Why the invoice block details not available during the invoice process under invoice block selection?

            The invoice block has already been created and all series are used. No unused series are available.

• Why is the Invoice not displayed in the dropdown list?

           The Invoice block has been created, but it is not associated with the respective cost center.

• Another reason why the invoice block is not visible during the invoice creation process is that the invoice block has not been created in the application.