Express Invoice 請求書作成ソフト - Can I add a letter (A,B,C) into the numeric Invoice Number field?

To customize your invoice numbering in Express Invoice:

Open Express Invoice.
Go to Settings > Invoice > Invoice Numbering > Prefix.
Enter the desired letter or prefix for your invoices.
Adjust the starting invoice number if necessary to avoid conflicts with existing invoices (as invoice numbers are generated sequentially).

Keep in mind that this change will be applied from the moment you set the prefix, and will not change existing invoices.

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